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 $209.99   8.671%   $228.1982   $228.20   $228.20   $228.20  
  Purchase #2 $59.53   4.263%   $62.0678   $62.07   $62.05   $62.10  
  Purchase #3 $161.44   7.487%   $173.527   $173.53   $173.55   $173.50  
  Purchase #4 $236.75   8.785%   $257.5485   $257.55   $257.55   $257.50  
  Purchase #5 $228.94   10.826%   $253.725   $253.73   $253.75   $253.70  
  Purchase #6 $7.91   11.753%   $8.8397   $8.84   $8.85   $8.80  
  Purchase #7 $44.87   6.134%   $47.6223   $47.62   $47.60   $47.60  
  7 purchase totals = $949.43       $1,031.5285   $1,031.54   $1,031.55   $1,031.40