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 $241.40   10.541%   $266.846   $266.85   $266.85   $266.80  
  Purchase #2 $60.98   13.703%   $69.3361   $69.34   $69.35   $69.30  
  Purchase #3 $32.25   4.735%   $33.777   $33.78   $33.80   $33.80  
  Purchase #4 $188.82   7.186%   $202.3886   $202.39   $202.40   $202.40  
  Purchase #5 $28.53   12.754%   $32.1687   $32.17   $32.15   $32.20  
  Purchase #6 $127.56   5.199%   $134.1918   $134.19   $134.20   $134.20  
  Purchase #7 $187.74   9.775%   $206.0916   $206.09   $206.10   $206.10  
  7 purchase totals = $867.28       $944.7998   $944.81   $944.85   $944.80