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 $183.28   11.826%   $204.9547   $204.95   $204.95   $205.00  
  Purchase #2 $20.87   12.137%   $23.403   $23.40   $23.40   $23.40  
  Purchase #3 $212.34   13.194%   $240.3561   $240.36   $240.35   $240.40  
  Purchase #4 $92.61   5.866%   $98.0425   $98.04   $98.05   $98.00  
  Purchase #5 $159.80   5.607%   $168.76   $168.76   $168.75   $168.80  
  Purchase #6 $18.47   8.163%   $19.9777   $19.98   $20.00   $20.00  
  Purchase #7 $133.96   11.361%   $149.1792   $149.18   $149.20   $149.20  
  7 purchase totals = $821.33       $904.6732   $904.67   $904.70   $904.80