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 $112.62   5.661%   $118.9954   $119.00   $119.00   $119.00  
  Purchase #2 $199.73   7.278%   $214.2663   $214.27   $214.25   $214.30  
  Purchase #3 $52.56   3.617%   $54.4611   $54.46   $54.45   $54.50  
  Purchase #4 $133.69   12.157%   $149.9427   $149.94   $149.95   $149.90  
  Purchase #5 $19.29   13.594%   $21.9123   $21.91   $21.90   $21.90  
  Purchase #6 $151.63   13.386%   $171.9272   $171.93   $171.95   $171.90  
  Purchase #7 $221.53   11.714%   $247.48   $247.48   $247.50   $247.50  
  7 purchase totals = $891.05       $978.9850   $978.99   $979.00   $979.00