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 $218.82   13.448%   $248.2469   $248.25   $248.25   $248.20  
  Purchase #2 $182.35   10.404%   $201.3217   $201.32   $201.30   $201.30  
  Purchase #3 $26.45   9.802%   $29.0426   $29.04   $29.05   $29.00  
  Purchase #4 $54.85   3.823%   $56.9469   $56.95   $56.95   $56.90  
  Purchase #5 $232.75   11.781%   $260.1703   $260.17   $260.15   $260.20  
  Purchase #6 $168.71   5.766%   $178.4378   $178.44   $178.45   $178.40  
  Purchase #7 $136.31   11.515%   $152.0061   $152.01   $152.00   $152.00  
  7 purchase totals = $1,020.24       $1,126.1723   $1,126.18   $1,126.15   $1,126.00