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 $202.39   8.630%   $219.8563   $219.86   $219.85   $219.90  
  Purchase #2 $11.51   3.231%   $11.8819   $11.88   $11.90   $11.90  
  Purchase #3 $125.75   7.446%   $135.1133   $135.11   $135.10   $135.10  
  Purchase #4 $58.63   6.705%   $62.5611   $62.56   $62.55   $62.60  
  Purchase #5 $249.60   5.493%   $263.3105   $263.31   $263.30   $263.30  
  Purchase #6 $51.31   3.762%   $53.2403   $53.24   $53.25   $53.20  
  Purchase #7 $173.97   12.362%   $195.4762   $195.48   $195.50   $195.50  
  7 purchase totals = $873.16       $941.4396   $941.44   $941.45   $941.50