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 $107.91   10.406%   $119.1391   $119.14   $119.15   $119.10  
  Purchase #2 $197.61   11.565%   $220.4636   $220.46   $220.45   $220.50  
  Purchase #3 $68.66   11.403%   $76.4893   $76.49   $76.50   $76.50  
  Purchase #4 $215.33   9.832%   $236.5012   $236.50   $236.50   $236.50  
  Purchase #5 $131.61   7.361%   $141.2978   $141.30   $141.30   $141.30  
  Purchase #6 $211.56   4.615%   $221.3235   $221.32   $221.30   $221.30  
  Purchase #7 $18.35   10.825%   $20.3364   $20.34   $20.35   $20.30  
  7 purchase totals = $951.03       $1,035.5509   $1,035.55   $1,035.55   $1,035.50