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 $180.33   7.756%   $194.3164   $194.32   $194.30   $194.30  
  Purchase #2 $22.42   5.499%   $23.6529   $23.65   $23.65   $23.70  
  Purchase #3 $115.63   12.664%   $130.2734   $130.27   $130.25   $130.30  
  Purchase #4 $86.89   10.755%   $96.235   $96.24   $96.25   $96.20  
  Purchase #5 $150.60   11.832%   $168.419   $168.42   $168.40   $168.40  
  Purchase #6 $223.97   5.540%   $236.3779   $236.38   $236.40   $236.40  
  Purchase #7 $110.68   6.599%   $117.9838   $117.98   $118.00   $118.00  
  7 purchase totals = $890.52       $967.2584   $967.26   $967.25   $967.30