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 $33.74   5.663%   $35.6507   $35.65   $35.65   $35.70  
  Purchase #2 $182.29   6.346%   $193.8581   $193.86   $193.85   $193.90  
  Purchase #3 $146.96   7.791%   $158.4097   $158.41   $158.40   $158.40  
  Purchase #4 $9.68   10.584%   $10.7045   $10.70   $10.70   $10.70  
  Purchase #5 $224.90   11.427%   $250.5993   $250.60   $250.60   $250.60  
  Purchase #6 $239.90   13.327%   $271.8715   $271.87   $271.85   $271.90  
  Purchase #7 $243.92   5.449%   $257.2112   $257.21   $257.20   $257.20  
  7 purchase totals = $1,081.39       $1,178.3050   $1,178.30   $1,178.25   $1,178.40