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 $224.46   13.813%   $255.4647   $255.46   $255.45   $255.50  
  Purchase #2 $157.87   7.223%   $169.273   $169.27   $169.25   $169.30  
  Purchase #3 $125.36   12.822%   $141.4337   $141.43   $141.45   $141.40  
  Purchase #4 $186.63   4.484%   $194.9985   $195.00   $195.00   $195.00  
  Purchase #5 $69.39   4.835%   $72.745   $72.75   $72.75   $72.70  
  Purchase #6 $171.69   3.841%   $178.2846   $178.28   $178.30   $178.30  
  Purchase #7 $247.76   6.813%   $264.6399   $264.64   $264.65   $264.60  
  7 purchase totals = $1,183.16       $1,276.8394   $1,276.83   $1,276.85   $1,276.80