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 $119.53   8.166%   $129.2908   $129.29   $129.30   $129.30  
  Purchase #2 $61.63   13.833%   $70.1553   $70.16   $70.15   $70.20  
  Purchase #3 $199.89   8.542%   $216.9646   $216.96   $216.95   $217.00  
  Purchase #4 $24.39   8.737%   $26.521   $26.52   $26.50   $26.50  
  Purchase #5 $52.42   9.517%   $57.4088   $57.41   $57.40   $57.40  
  Purchase #6 $6.60   5.126%   $6.9383   $6.94   $6.95   $6.90  
  Purchase #7 $187.28   9.791%   $205.6166   $205.62   $205.60   $205.60  
  7 purchase totals = $651.74       $712.8954   $712.90   $712.85   $712.90