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 $94.59   13.136%   $107.0153   $107.02   $107.00   $107.00  
  Purchase #2 $212.35   9.496%   $232.5148   $232.51   $232.50   $232.50  
  Purchase #3 $16.65   10.132%   $18.337   $18.34   $18.35   $18.30  
  Purchase #4 $132.69   4.668%   $138.884   $138.88   $138.90   $138.90  
  Purchase #5 $20.47   5.400%   $21.5754   $21.58   $21.60   $21.60  
  Purchase #6 $90.66   10.269%   $99.9699   $99.97   $99.95   $100.00  
  Purchase #7 $236.68   8.559%   $256.9374   $256.94   $256.95   $256.90  
  7 purchase totals = $804.09       $875.2338   $875.24   $875.25   $875.20