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 $45.52   7.520%   $48.9431   $48.94   $48.95   $48.90  
  Purchase #2 $239.94   11.528%   $267.6003   $267.60   $267.60   $267.60  
  Purchase #3 $113.85   12.643%   $128.2441   $128.24   $128.25   $128.20  
  Purchase #4 $178.49   13.502%   $202.5897   $202.59   $202.60   $202.60  
  Purchase #5 $23.27   6.403%   $24.76   $24.76   $24.75   $24.80  
  Purchase #6 $75.43   3.715%   $78.2322   $78.23   $78.25   $78.20  
  Purchase #7 $42.62   10.177%   $46.9574   $46.96   $46.95   $47.00  
  7 purchase totals = $719.12       $797.3268   $797.32   $797.35   $797.30