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 $14.93   13.439%   $16.9364   $16.94   $16.95   $16.90  
  Purchase #2 $223.63   5.277%   $235.431   $235.43   $235.45   $235.40  
  Purchase #3 $125.87   10.446%   $139.0184   $139.02   $139.00   $139.00  
  Purchase #4 $13.49   3.121%   $13.911   $13.91   $13.90   $13.90  
  Purchase #5 $247.43   3.171%   $255.276   $255.28   $255.30   $255.30  
  Purchase #6 $202.68   3.668%   $210.1143   $210.11   $210.10   $210.10  
  Purchase #7 $86.95   9.139%   $94.8964   $94.90   $94.90   $94.90  
  7 purchase totals = $914.98       $965.5835   $965.59   $965.60   $965.50