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 $68.91   13.703%   $78.3527   $78.35   $78.35   $78.40  
  Purchase #2 $225.60   9.842%   $247.8036   $247.80   $247.80   $247.80  
  Purchase #3 $175.77   10.122%   $193.5614   $193.56   $193.55   $193.60  
  Purchase #4 $11.91   13.590%   $13.5286   $13.53   $13.55   $13.50  
  Purchase #5 $177.39   8.266%   $192.0531   $192.05   $192.05   $192.10  
  Purchase #6 $72.45   6.757%   $77.3454   $77.35   $77.35   $77.30  
  Purchase #7 $75.76   6.785%   $80.9003   $80.90   $80.90   $80.90  
  7 purchase totals = $807.79       $883.5451   $883.54   $883.55   $883.60