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 $245.85   8.286%   $266.2211   $266.22   $266.20   $266.20  
  Purchase #2 $43.64   6.317%   $46.3967   $46.40   $46.40   $46.40  
  Purchase #3 $76.56   9.453%   $83.7972   $83.80   $83.80   $83.80  
  Purchase #4 $125.37   11.484%   $139.7675   $139.77   $139.75   $139.80  
  Purchase #5 $76.35   10.200%   $84.1377   $84.14   $84.15   $84.10  
  Purchase #6 $210.51   10.636%   $232.8998   $232.90   $232.90   $232.90  
  Purchase #7 $171.31   9.826%   $188.1429   $188.14   $188.15   $188.10  
  7 purchase totals = $949.59       $1,041.3629   $1,041.37   $1,041.35   $1,041.30