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 $235.69   13.266%   $266.9566   $266.96   $266.95   $267.00  
  Purchase #2 $54.71   8.762%   $59.5037   $59.50   $59.50   $59.50  
  Purchase #3 $20.32   12.517%   $22.8635   $22.86   $22.85   $22.90  
  Purchase #4 $200.43   11.429%   $223.3371   $223.34   $223.35   $223.30  
  Purchase #5 $177.94   5.203%   $187.1982   $187.20   $187.20   $187.20  
  Purchase #6 $189.71   4.260%   $197.7916   $197.79   $197.80   $197.80  
  Purchase #7 $22.66   12.681%   $25.5335   $25.53   $25.55   $25.50  
  7 purchase totals = $901.46       $983.1842   $983.18   $983.20   $983.20