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 $241.42   6.106%   $256.1611   $256.16   $256.15   $256.20  
  Purchase #2 $246.40   10.126%   $271.3505   $271.35   $271.35   $271.40  
  Purchase #3 $164.73   3.105%   $169.8449   $169.84   $169.85   $169.80  
  Purchase #4 $57.38   10.190%   $63.227   $63.23   $63.25   $63.20  
  Purchase #5 $228.87   6.513%   $243.7763   $243.78   $243.80   $243.80  
  Purchase #6 $206.69   5.344%   $217.7355   $217.74   $217.75   $217.70  
  Purchase #7 $120.60   5.810%   $127.6069   $127.61   $127.60   $127.60  
  7 purchase totals = $1,266.09       $1,349.7022   $1,349.71   $1,349.75   $1,349.70