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 $232.74   9.154%   $254.045   $254.05   $254.05   $254.00  
  Purchase #2 $36.98   13.863%   $42.1065   $42.11   $42.10   $42.10  
  Purchase #3 $29.79   5.474%   $31.4207   $31.42   $31.40   $31.40  
  Purchase #4 $21.49   3.639%   $22.272   $22.27   $22.25   $22.30  
  Purchase #5 $239.78   9.345%   $262.1874   $262.19   $262.20   $262.20  
  Purchase #6 $195.91   5.452%   $206.591   $206.59   $206.60   $206.60  
  Purchase #7 $194.74   8.785%   $211.8479   $211.85   $211.85   $211.80  
  7 purchase totals = $951.43       $1,030.4705   $1,030.48   $1,030.45   $1,030.40