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 $87.98   6.136%   $93.3785   $93.38   $93.40   $93.40  
  Purchase #2 $189.51   3.410%   $195.9723   $195.97   $195.95   $196.00  
  Purchase #3 $174.35   5.722%   $184.3263   $184.33   $184.35   $184.30  
  Purchase #4 $188.97   6.309%   $200.8921   $200.89   $200.90   $200.90  
  Purchase #5 $61.99   12.769%   $69.9055   $69.91   $69.90   $69.90  
  Purchase #6 $12.26   10.778%   $13.5814   $13.58   $13.60   $13.60  
  Purchase #7 $165.81   11.556%   $184.971   $184.97   $184.95   $185.00  
  7 purchase totals = $880.87       $943.0271   $943.03   $943.05   $943.10