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 $61.90   10.783%   $68.5747   $68.57   $68.55   $68.60  
  Purchase #2 $12.28   4.763%   $12.8649   $12.86   $12.85   $12.90  
  Purchase #3 $48.68   6.289%   $51.7415   $51.74   $51.75   $51.70  
  Purchase #4 $150.72   3.684%   $156.2725   $156.27   $156.25   $156.30  
  Purchase #5 $245.59   11.671%   $274.2528   $274.25   $274.25   $274.30  
  Purchase #6 $217.39   9.191%   $237.3703   $237.37   $237.35   $237.40  
  Purchase #7 $86.44   7.829%   $93.2074   $93.21   $93.20   $93.20  
  7 purchase totals = $823.00       $894.2841   $894.27   $894.20   $894.40