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 $236.62   13.494%   $268.5495   $268.55   $268.55   $268.50  
  Purchase #2 $170.55   6.865%   $182.2583   $182.26   $182.25   $182.30  
  Purchase #3 $69.55   4.865%   $72.9336   $72.93   $72.95   $72.90  
  Purchase #4 $127.53   6.196%   $135.4318   $135.43   $135.45   $135.40  
  Purchase #5 $64.71   7.248%   $69.4002   $69.40   $69.40   $69.40  
  Purchase #6 $20.96   5.446%   $22.1015   $22.10   $22.10   $22.10  
  Purchase #7 $195.59   3.562%   $202.5569   $202.56   $202.55   $202.60  
  7 purchase totals = $885.51       $953.2318   $953.23   $953.25   $953.20