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 $203.57   9.646%   $223.2064   $223.21   $223.20   $223.20  
  Purchase #2 $121.49   9.368%   $132.8712   $132.87   $132.85   $132.90  
  Purchase #3 $178.35   8.249%   $193.0621   $193.06   $193.05   $193.10  
  Purchase #4 $242.74   10.354%   $267.8733   $267.87   $267.85   $267.90  
  Purchase #5 $122.69   6.252%   $130.3606   $130.36   $130.35   $130.40  
  Purchase #6 $244.25   7.387%   $262.2927   $262.29   $262.30   $262.30  
  Purchase #7 $225.28   13.216%   $255.053   $255.05   $255.05   $255.10  
  7 purchase totals = $1,338.37       $1,464.7193   $1,464.71   $1,464.65   $1,464.90