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 $227.25   11.831%   $254.1359   $254.14   $254.15   $254.10  
  Purchase #2 $184.43   10.106%   $203.0685   $203.07   $203.05   $203.10  
  Purchase #3 $31.73   8.791%   $34.5194   $34.52   $34.50   $34.50  
  Purchase #4 $21.35   11.839%   $23.8776   $23.88   $23.90   $23.90  
  Purchase #5 $93.50   9.314%   $102.2086   $102.21   $102.20   $102.20  
  Purchase #6 $204.27   6.714%   $217.9847   $217.98   $218.00   $218.00  
  Purchase #7 $114.78   4.340%   $119.7615   $119.76   $119.75   $119.80  
  7 purchase totals = $877.31       $955.5562   $955.56   $955.55   $955.60