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 $84.67   10.492%   $93.5536   $93.55   $93.55   $93.60  
  Purchase #2 $59.48   11.175%   $66.1269   $66.13   $66.15   $66.10  
  Purchase #3 $107.43   10.684%   $118.9078   $118.91   $118.90   $118.90  
  Purchase #4 $93.40   7.431%   $100.3406   $100.34   $100.35   $100.30  
  Purchase #5 $40.62   6.670%   $43.3294   $43.33   $43.35   $43.30  
  Purchase #6 $240.99   4.739%   $252.4105   $252.41   $252.40   $252.40  
  Purchase #7 $166.54   4.435%   $173.926   $173.93   $173.95   $173.90  
  7 purchase totals = $793.13       $848.5948   $848.60   $848.65   $848.50