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 $114.35   4.232%   $119.1893   $119.19   $119.20   $119.20  
  Purchase #2 $207.30   6.598%   $220.9777   $220.98   $221.00   $221.00  
  Purchase #3 $25.80   8.674%   $28.0379   $28.04   $28.05   $28.00  
  Purchase #4 $53.41   7.645%   $57.4932   $57.49   $57.50   $57.50  
  Purchase #5 $130.94   6.318%   $139.2128   $139.21   $139.20   $139.20  
  Purchase #6 $167.61   11.811%   $187.4064   $187.41   $187.40   $187.40  
  Purchase #7 $56.78   13.241%   $64.2982   $64.30   $64.30   $64.30  
  7 purchase totals = $756.19       $816.6155   $816.62   $816.65   $816.60