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 $56.51   5.239%   $59.4706   $59.47   $59.45   $59.50  
  Purchase #2 $28.98   9.536%   $31.7435   $31.74   $31.75   $31.70  
  Purchase #3 $89.56   6.414%   $95.3044   $95.30   $95.30   $95.30  
  Purchase #4 $107.44   5.776%   $113.6457   $113.65   $113.65   $113.60  
  Purchase #5 $148.80   9.804%   $163.3884   $163.39   $163.40   $163.40  
  Purchase #6 $51.50   10.400%   $56.856   $56.86   $56.85   $56.90  
  Purchase #7 $188.99   9.290%   $206.5472   $206.55   $206.55   $206.50  
  7 purchase totals = $671.78       $726.9558   $726.96   $726.95   $726.90