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 $59.94   13.805%   $68.2147   $68.21   $68.20   $68.20  
  Purchase #2 $71.95   3.327%   $74.3438   $74.34   $74.35   $74.30  
  Purchase #3 $54.65   7.844%   $58.9367   $58.94   $58.95   $58.90  
  Purchase #4 $250.93   6.561%   $267.3935   $267.39   $267.40   $267.40  
  Purchase #5 $44.78   7.312%   $48.0543   $48.05   $48.05   $48.10  
  Purchase #6 $108.72   13.656%   $123.5668   $123.57   $123.55   $123.60  
  Purchase #7 $95.52   7.201%   $102.3984   $102.40   $102.40   $102.40  
  7 purchase totals = $686.49       $742.9082   $742.90   $742.90   $742.90