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 $235.56   12.537%   $265.0922   $265.09   $265.10   $265.10  
  Purchase #2 $222.44   9.398%   $243.3449   $243.34   $243.35   $243.30  
  Purchase #3 $161.41   8.357%   $174.899   $174.90   $174.90   $174.90  
  Purchase #4 $46.55   3.463%   $48.162   $48.16   $48.15   $48.20  
  Purchase #5 $175.40   11.240%   $195.115   $195.12   $195.10   $195.10  
  Purchase #6 $51.37   6.193%   $54.5513   $54.55   $54.55   $54.60  
  Purchase #7 $29.97   13.590%   $34.0429   $34.04   $34.05   $34.00  
  7 purchase totals = $922.70       $1,015.2073   $1,015.20   $1,015.20   $1,015.20