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 $219.99   12.367%   $247.1962   $247.20   $247.20   $247.20  
  Purchase #2 $192.73   5.138%   $202.6325   $202.63   $202.65   $202.60  
  Purchase #3 $167.68   11.339%   $186.6932   $186.69   $186.70   $186.70  
  Purchase #4 $92.82   13.175%   $105.049   $105.05   $105.05   $105.00  
  Purchase #5 $118.70   12.143%   $133.1137   $133.11   $133.10   $133.10  
  Purchase #6 $215.56   4.765%   $225.8314   $225.83   $225.85   $225.80  
  Purchase #7 $65.79   5.618%   $69.4861   $69.49   $69.50   $69.50  
  7 purchase totals = $1,073.27       $1,170.0021   $1,170.00   $1,170.05   $1,169.90