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 $82.32   6.327%   $87.5284   $87.53   $87.55   $87.50  
  Purchase #2 $224.78   5.145%   $236.3449   $236.34   $236.35   $236.30  
  Purchase #3 $24.70   4.681%   $25.8562   $25.86   $25.85   $25.90  
  Purchase #4 $84.97   6.170%   $90.2126   $90.21   $90.20   $90.20  
  Purchase #5 $161.29   5.677%   $170.4464   $170.45   $170.45   $170.40  
  Purchase #6 $211.45   9.783%   $232.1362   $232.14   $232.15   $232.10  
  Purchase #7 $117.63   6.636%   $125.4359   $125.44   $125.45   $125.40  
  7 purchase totals = $907.14       $967.9606   $967.97   $968.00   $967.80