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 $85.39   9.588%   $93.5772   $93.58   $93.60   $93.60  
  Purchase #2 $228.81   3.504%   $236.8275   $236.83   $236.85   $236.80  
  Purchase #3 $11.95   10.609%   $13.2178   $13.22   $13.20   $13.20  
  Purchase #4 $224.83   11.608%   $250.9283   $250.93   $250.95   $250.90  
  Purchase #5 $249.31   10.565%   $275.6496   $275.65   $275.65   $275.60  
  Purchase #6 $97.54   4.267%   $101.702   $101.70   $101.70   $101.70  
  Purchase #7 $228.31   6.581%   $243.3351   $243.34   $243.35   $243.30  
  7 purchase totals = $1,126.14       $1,215.2375   $1,215.25   $1,215.30   $1,215.10