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 $213.93   6.124%   $227.0311   $227.03   $227.05   $227.00  
  Purchase #2 $195.72   4.416%   $204.363   $204.36   $204.35   $204.40  
  Purchase #3 $128.53   4.118%   $133.8229   $133.82   $133.80   $133.80  
  Purchase #4 $77.68   5.563%   $82.0013   $82.00   $82.00   $82.00  
  Purchase #5 $148.36   13.612%   $168.5548   $168.55   $168.55   $168.60  
  Purchase #6 $32.75   12.522%   $36.851   $36.85   $36.85   $36.90  
  Purchase #7 $75.40   3.105%   $77.7412   $77.74   $77.75   $77.70  
  7 purchase totals = $872.37       $930.3653   $930.35   $930.35   $930.40