Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.47   8.277%   $223.5595   $223.56   $223.55   $223.60  
  Purchase #2 $143.54   13.339%   $162.6868   $162.69   $162.70   $162.70  
  Purchase #3 $218.33   13.474%   $247.7478   $247.75   $247.75   $247.70  
  Purchase #4 $213.27   6.221%   $226.5375   $226.54   $226.55   $226.50  
  Purchase #5 $206.64   4.569%   $216.0814   $216.08   $216.10   $216.10  
  Purchase #6 $118.68   11.267%   $132.0517   $132.05   $132.05   $132.10  
  Purchase #7 $241.79   13.307%   $273.965   $273.97   $273.95   $274.00  
  7 purchase totals = $1,348.72       $1,482.6297   $1,482.64   $1,482.65   $1,482.70