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 $59.25   6.304%   $62.9851   $62.99   $63.00   $63.00  
  Purchase #2 $80.48   9.761%   $88.3357   $88.34   $88.35   $88.30  
  Purchase #3 $41.61   7.289%   $44.643   $44.64   $44.65   $44.60  
  Purchase #4 $213.65   3.608%   $221.3585   $221.36   $221.35   $221.40  
  Purchase #5 $222.98   11.475%   $248.567   $248.57   $248.55   $248.60  
  Purchase #6 $35.88   6.359%   $38.1616   $38.16   $38.15   $38.20  
  Purchase #7 $217.41   12.476%   $244.5341   $244.53   $244.55   $244.50  
  7 purchase totals = $871.26       $948.5850   $948.59   $948.60   $948.60