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 $64.97   13.379%   $73.6623   $73.66   $73.65   $73.70  
  Purchase #2 $47.77   8.685%   $51.9188   $51.92   $51.90   $51.90  
  Purchase #3 $37.53   9.196%   $40.9813   $40.98   $41.00   $41.00  
  Purchase #4 $236.49   12.265%   $265.4955   $265.50   $265.50   $265.50  
  Purchase #5 $180.25   5.185%   $189.596   $189.60   $189.60   $189.60  
  Purchase #6 $195.99   11.843%   $219.2011   $219.20   $219.20   $219.20  
  Purchase #7 $112.36   13.581%   $127.6196   $127.62   $127.60   $127.60  
  7 purchase totals = $875.36       $968.4746   $968.48   $968.45   $968.50