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 $208.34   12.803%   $235.0138   $235.01   $235.00   $235.00  
  Purchase #2 $61.42   8.175%   $66.4411   $66.44   $66.45   $66.40  
  Purchase #3 $222.62   6.235%   $236.5004   $236.50   $236.50   $236.50  
  Purchase #4 $162.85   8.424%   $176.5685   $176.57   $176.55   $176.60  
  Purchase #5 $34.57   10.638%   $38.2476   $38.25   $38.25   $38.20  
  Purchase #6 $213.87   5.339%   $225.2885   $225.29   $225.30   $225.30  
  Purchase #7 $244.81   11.723%   $273.5091   $273.51   $273.50   $273.50  
  7 purchase totals = $1,148.48       $1,251.5690   $1,251.57   $1,251.55   $1,251.50