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 $47.61   6.286%   $50.6028   $50.60   $50.60   $50.60  
  Purchase #2 $116.38   13.813%   $132.4556   $132.46   $132.45   $132.50  
  Purchase #3 $10.40   5.270%   $10.9481   $10.95   $10.95   $10.90  
  Purchase #4 $57.67   5.300%   $60.7265   $60.73   $60.75   $60.70  
  Purchase #5 $99.52   5.355%   $104.8493   $104.85   $104.85   $104.80  
  Purchase #6 $134.36   5.202%   $141.3494   $141.35   $141.35   $141.30  
  Purchase #7 $247.95   6.634%   $264.399   $264.40   $264.40   $264.40  
  7 purchase totals = $713.89       $765.3307   $765.34   $765.35   $765.20