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 $98.85   4.781%   $103.576   $103.58   $103.60   $103.60  
  Purchase #2 $152.36   9.382%   $166.6544   $166.65   $166.65   $166.70  
  Purchase #3 $62.43   8.301%   $67.6123   $67.61   $67.60   $67.60  
  Purchase #4 $130.42   9.188%   $142.403   $142.40   $142.40   $142.40  
  Purchase #5 $112.33   11.510%   $125.2592   $125.26   $125.25   $125.30  
  Purchase #6 $45.84   10.532%   $50.6679   $50.67   $50.65   $50.70  
  Purchase #7 $156.90   11.349%   $174.7066   $174.71   $174.70   $174.70  
  7 purchase totals = $759.13       $830.8794   $830.88   $830.85   $831.00