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 $232.54   10.498%   $256.952   $256.95   $256.95   $257.00  
  Purchase #2 $119.71   11.460%   $133.4288   $133.43   $133.45   $133.40  
  Purchase #3 $33.71   7.707%   $36.308   $36.31   $36.30   $36.30  
  Purchase #4 $70.57   6.728%   $75.3179   $75.32   $75.30   $75.30  
  Purchase #5 $167.97   4.204%   $175.0315   $175.03   $175.05   $175.00  
  Purchase #6 $62.64   10.788%   $69.3976   $69.40   $69.40   $69.40  
  Purchase #7 $226.40   10.706%   $250.6384   $250.64   $250.65   $250.60  
  7 purchase totals = $913.54       $997.0742   $997.08   $997.10   $997.00