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 $250.59   9.620%   $274.6968   $274.70   $274.70   $274.70  
  Purchase #2 $244.85   12.599%   $275.6987   $275.70   $275.70   $275.70  
  Purchase #3 $155.70   9.716%   $170.8278   $170.83   $170.85   $170.80  
  Purchase #4 $6.73   6.155%   $7.1442   $7.14   $7.15   $7.10  
  Purchase #5 $23.93   5.137%   $25.1593   $25.16   $25.15   $25.20  
  Purchase #6 $52.26   13.135%   $59.1244   $59.12   $59.10   $59.10  
  Purchase #7 $160.38   5.596%   $169.3549   $169.35   $169.35   $169.40  
  7 purchase totals = $894.44       $982.0061   $982.00   $982.00   $982.00