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 $231.66   6.756%   $247.3109   $247.31   $247.30   $247.30  
  Purchase #2 $176.75   10.496%   $195.3017   $195.30   $195.30   $195.30  
  Purchase #3 $188.66   8.659%   $204.9961   $205.00   $205.00   $205.00  
  Purchase #4 $139.31   11.657%   $155.5494   $155.55   $155.55   $155.50  
  Purchase #5 $32.38   12.307%   $36.365   $36.37   $36.35   $36.40  
  Purchase #6 $108.28   6.568%   $115.3918   $115.39   $115.40   $115.40  
  Purchase #7 $70.47   11.648%   $78.6783   $78.68   $78.70   $78.70  
  7 purchase totals = $947.51       $1,033.5932   $1,033.60   $1,033.60   $1,033.60