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 $54.37   11.707%   $60.7351   $60.74   $60.75   $60.70  
  Purchase #2 $74.73   6.293%   $79.4328   $79.43   $79.45   $79.40  
  Purchase #3 $157.45   3.383%   $162.7765   $162.78   $162.80   $162.80  
  Purchase #4 $127.29   3.832%   $132.1678   $132.17   $132.15   $132.20  
  Purchase #5 $188.92   4.811%   $198.0089   $198.01   $198.00   $198.00  
  Purchase #6 $152.95   11.540%   $170.6004   $170.60   $170.60   $170.60  
  Purchase #7 $56.53   6.122%   $59.9908   $59.99   $60.00   $60.00  
  7 purchase totals = $812.24       $863.7123   $863.72   $863.75   $863.70