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 $56.63   12.657%   $63.7977   $63.80   $63.80   $63.80  
  Purchase #2 $199.73   4.453%   $208.624   $208.62   $208.60   $208.60  
  Purchase #3 $60.43   10.138%   $66.5564   $66.56   $66.55   $66.60  
  Purchase #4 $44.75   13.316%   $50.7089   $50.71   $50.70   $50.70  
  Purchase #5 $93.98   10.282%   $103.643   $103.64   $103.65   $103.60  
  Purchase #6 $180.64   4.785%   $189.2836   $189.28   $189.30   $189.30  
  Purchase #7 $20.41   9.684%   $22.3865   $22.39   $22.40   $22.40  
  7 purchase totals = $656.57       $705.0001   $705.00   $705.00   $705.00