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 $177.73   13.105%   $201.0215   $201.02   $201.00   $201.00  
  Purchase #2 $48.84   6.341%   $51.9369   $51.94   $51.95   $51.90  
  Purchase #3 $239.77   13.417%   $271.9399   $271.94   $271.95   $271.90  
  Purchase #4 $33.65   5.778%   $35.5943   $35.59   $35.60   $35.60  
  Purchase #5 $178.84   9.837%   $196.4325   $196.43   $196.45   $196.40  
  Purchase #6 $137.68   11.867%   $154.0185   $154.02   $154.00   $154.00  
  Purchase #7 $111.65   7.452%   $119.9702   $119.97   $119.95   $120.00  
  7 purchase totals = $928.16       $1,030.9138   $1,030.91   $1,030.90   $1,030.80