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 $113.78   6.571%   $121.2565   $121.26   $121.25   $121.30  
  Purchase #2 $86.91   11.557%   $96.9542   $96.95   $96.95   $97.00  
  Purchase #3 $223.92   9.425%   $245.0245   $245.02   $245.00   $245.00  
  Purchase #4 $141.88   12.500%   $159.615   $159.62   $159.60   $159.60  
  Purchase #5 $241.71   6.794%   $258.1318   $258.13   $258.15   $258.10  
  Purchase #6 $84.92   13.122%   $96.0632   $96.06   $96.05   $96.10  
  Purchase #7 $62.60   10.617%   $69.2462   $69.25   $69.25   $69.20  
  7 purchase totals = $955.72       $1,046.2914   $1,046.29   $1,046.25   $1,046.30