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 $106.65   10.651%   $118.0093   $118.01   $118.00   $118.00  
  Purchase #2 $25.83   4.522%   $26.998   $27.00   $27.00   $27.00  
  Purchase #3 $48.27   4.159%   $50.2775   $50.28   $50.30   $50.30  
  Purchase #4 $68.75   12.666%   $77.4579   $77.46   $77.45   $77.50  
  Purchase #5 $249.94   11.303%   $278.1907   $278.19   $278.20   $278.20  
  Purchase #6 $196.66   4.406%   $205.3248   $205.32   $205.30   $205.30  
  Purchase #7 $197.82   7.451%   $212.5596   $212.56   $212.55   $212.60  
  7 purchase totals = $893.92       $968.8178   $968.82   $968.80   $968.90