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 $36.76   11.663%   $41.0473   $41.05   $41.05   $41.00  
  Purchase #2 $134.39   3.502%   $139.0963   $139.10   $139.10   $139.10  
  Purchase #3 $92.40   11.266%   $102.8098   $102.81   $102.80   $102.80  
  Purchase #4 $92.61   4.636%   $96.9034   $96.90   $96.90   $96.90  
  Purchase #5 $177.53   4.334%   $185.2242   $185.22   $185.20   $185.20  
  Purchase #6 $127.96   10.214%   $141.0298   $141.03   $141.05   $141.00  
  Purchase #7 $216.37   6.643%   $230.7435   $230.74   $230.75   $230.70  
  7 purchase totals = $878.02       $936.8543   $936.85   $936.85   $936.70