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 $229.53   11.248%   $255.3475   $255.35   $255.35   $255.30  
  Purchase #2 $217.71   12.211%   $244.2946   $244.29   $244.30   $244.30  
  Purchase #3 $164.76   5.758%   $174.2469   $174.25   $174.25   $174.20  
  Purchase #4 $123.88   10.139%   $136.4402   $136.44   $136.45   $136.40  
  Purchase #5 $195.26   5.488%   $205.9759   $205.98   $206.00   $206.00  
  Purchase #6 $150.50   12.741%   $169.6752   $169.68   $169.70   $169.70  
  Purchase #7 $8.51   3.178%   $8.7804   $8.78   $8.80   $8.80  
  7 purchase totals = $1,090.15       $1,194.7607   $1,194.77   $1,194.85   $1,194.70