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 $83.66   13.599%   $95.0369   $95.04   $95.05   $95.00  
  Purchase #2 $169.88   6.449%   $180.8356   $180.84   $180.85   $180.80  
  Purchase #3 $185.55   13.335%   $210.2931   $210.29   $210.30   $210.30  
  Purchase #4 $200.76   4.149%   $209.0895   $209.09   $209.10   $209.10  
  Purchase #5 $237.55   8.814%   $258.4877   $258.49   $258.50   $258.50  
  Purchase #6 $82.98   11.686%   $92.677   $92.68   $92.70   $92.70  
  Purchase #7 $213.41   11.224%   $237.3631   $237.36   $237.35   $237.40  
  7 purchase totals = $1,173.79       $1,283.7829   $1,283.79   $1,283.85   $1,283.80