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 $91.61   6.616%   $97.6709   $97.67   $97.65   $97.70  
  Purchase #2 $151.25   11.358%   $168.429   $168.43   $168.45   $168.40  
  Purchase #3 $70.58   6.202%   $74.9574   $74.96   $74.95   $75.00  
  Purchase #4 $78.34   12.316%   $87.9884   $87.99   $88.00   $88.00  
  Purchase #5 $111.83   7.544%   $120.2665   $120.27   $120.25   $120.30  
  Purchase #6 $67.91   10.512%   $75.0487   $75.05   $75.05   $75.00  
  Purchase #7 $239.73   10.682%   $265.338   $265.34   $265.35   $265.30  
  7 purchase totals = $811.25       $889.6989   $889.71   $889.70   $889.70