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 $149.36   4.858%   $156.6159   $156.62   $156.60   $156.60  
  Purchase #2 $247.33   10.593%   $273.5297   $273.53   $273.55   $273.50  
  Purchase #3 $249.32   10.183%   $274.7083   $274.71   $274.70   $274.70  
  Purchase #4 $203.60   6.416%   $216.663   $216.66   $216.65   $216.70  
  Purchase #5 $68.79   11.459%   $76.6726   $76.67   $76.65   $76.70  
  Purchase #6 $210.30   8.362%   $227.8853   $227.89   $227.90   $227.90  
  Purchase #7 $166.85   11.581%   $186.1729   $186.17   $186.15   $186.20  
  7 purchase totals = $1,295.55       $1,412.2477   $1,412.25   $1,412.20   $1,412.30