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 $201.56   6.766%   $215.1975   $215.20   $215.20   $215.20  
  Purchase #2 $119.57   4.762%   $125.2639   $125.26   $125.25   $125.30  
  Purchase #3 $119.40   5.442%   $125.8977   $125.90   $125.90   $125.90  
  Purchase #4 $250.85   7.430%   $269.4882   $269.49   $269.50   $269.50  
  Purchase #5 $116.53   8.416%   $126.3372   $126.34   $126.35   $126.30  
  Purchase #6 $16.49   6.174%   $17.5081   $17.51   $17.50   $17.50  
  Purchase #7 $81.77   10.507%   $90.3616   $90.36   $90.35   $90.40  
  7 purchase totals = $906.17       $970.0542   $970.06   $970.05   $970.10