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 $66.75   12.682%   $75.2152   $75.22   $75.20   $75.20  
  Purchase #2 $250.52   4.874%   $262.7303   $262.73   $262.75   $262.70  
  Purchase #3 $197.61   4.145%   $205.8009   $205.80   $205.80   $205.80  
  Purchase #4 $32.52   11.134%   $36.1408   $36.14   $36.15   $36.10  
  Purchase #5 $181.82   10.716%   $201.3038   $201.30   $201.30   $201.30  
  Purchase #6 $74.82   4.369%   $78.0889   $78.09   $78.10   $78.10  
  Purchase #7 $96.91   7.316%   $103.9999   $104.00   $104.00   $104.00  
  7 purchase totals = $900.95       $963.2798   $963.28   $963.30   $963.20