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 $168.94   11.497%   $188.363   $188.36   $188.35   $188.40  
  Purchase #2 $113.76   5.275%   $119.7608   $119.76   $119.75   $119.80  
  Purchase #3 $51.79   12.174%   $58.0949   $58.09   $58.10   $58.10  
  Purchase #4 $70.50   3.838%   $73.2058   $73.21   $73.20   $73.20  
  Purchase #5 $190.93   7.348%   $204.9595   $204.96   $204.95   $205.00  
  Purchase #6 $14.43   11.677%   $16.115   $16.12   $16.10   $16.10  
  Purchase #7 $185.34   3.695%   $192.1883   $192.19   $192.20   $192.20  
  7 purchase totals = $795.69       $852.6873   $852.69   $852.65   $852.80