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 $59.41   6.505%   $63.2746   $63.27   $63.25   $63.30  
  Purchase #2 $55.49   4.511%   $57.9932   $57.99   $58.00   $58.00  
  Purchase #3 $95.88   13.484%   $108.8085   $108.81   $108.80   $108.80  
  Purchase #4 $213.84   5.266%   $225.1008   $225.10   $225.10   $225.10  
  Purchase #5 $16.74   3.536%   $17.3319   $17.33   $17.35   $17.30  
  Purchase #6 $239.26   8.874%   $260.4919   $260.49   $260.50   $260.50  
  Purchase #7 $30.33   6.169%   $32.2011   $32.20   $32.20   $32.20  
  7 purchase totals = $710.95       $765.2020   $765.19   $765.20   $765.20