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 $240.34   8.217%   $260.0887   $260.09   $260.10   $260.10  
  Purchase #2 $19.48   4.665%   $20.3887   $20.39   $20.40   $20.40  
  Purchase #3 $182.49   7.373%   $195.945   $195.95   $195.95   $195.90  
  Purchase #4 $82.97   12.557%   $93.3885   $93.39   $93.40   $93.40  
  Purchase #5 $42.41   12.787%   $47.833   $47.83   $47.85   $47.80  
  Purchase #6 $248.96   11.184%   $276.8037   $276.80   $276.80   $276.80  
  Purchase #7 $151.74   4.158%   $158.0493   $158.05   $158.05   $158.00  
  7 purchase totals = $968.39       $1,052.4969   $1,052.50   $1,052.55   $1,052.40