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 $53.33   11.115%   $59.2576   $59.26   $59.25   $59.30  
  Purchase #2 $119.67   4.839%   $125.4608   $125.46   $125.45   $125.50  
  Purchase #3 $108.29   9.591%   $118.6761   $118.68   $118.70   $118.70  
  Purchase #4 $191.98   11.831%   $214.6932   $214.69   $214.70   $214.70  
  Purchase #5 $76.64   8.555%   $83.1966   $83.20   $83.20   $83.20  
  Purchase #6 $244.66   13.140%   $276.8083   $276.81   $276.80   $276.80  
  Purchase #7 $32.66   10.743%   $36.1687   $36.17   $36.15   $36.20  
  7 purchase totals = $827.23       $914.2613   $914.27   $914.25   $914.40