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 $92.71   6.617%   $98.8446   $98.84   $98.85   $98.80  
  Purchase #2 $209.34   13.611%   $237.8333   $237.83   $237.85   $237.80  
  Purchase #3 $123.96   9.838%   $136.1552   $136.16   $136.15   $136.20  
  Purchase #4 $66.97   6.669%   $71.4362   $71.44   $71.45   $71.40  
  Purchase #5 $66.30   13.366%   $75.1617   $75.16   $75.15   $75.20  
  Purchase #6 $203.26   7.229%   $217.9537   $217.95   $217.95   $218.00  
  Purchase #7 $187.85   8.532%   $203.8774   $203.88   $203.90   $203.90  
  7 purchase totals = $950.39       $1,041.2621   $1,041.26   $1,041.30   $1,041.30