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 $104.82   8.266%   $113.4844   $113.48   $113.50   $113.50  
  Purchase #2 $195.77   11.335%   $217.9605   $217.96   $217.95   $218.00  
  Purchase #3 $116.49   7.110%   $124.7724   $124.77   $124.75   $124.80  
  Purchase #4 $102.53   8.848%   $111.6019   $111.60   $111.60   $111.60  
  Purchase #5 $207.96   5.309%   $219.0006   $219.00   $219.00   $219.00  
  Purchase #6 $197.76   4.290%   $206.2439   $206.24   $206.25   $206.20  
  Purchase #7 $216.86   12.243%   $243.4102   $243.41   $243.40   $243.40  
  7 purchase totals = $1,142.19       $1,236.4739   $1,236.46   $1,236.45   $1,236.50