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 $223.98   3.711%   $232.2919   $232.29   $232.30   $232.30  
  Purchase #2 $161.68   11.385%   $180.0873   $180.09   $180.10   $180.10  
  Purchase #3 $13.84   10.175%   $15.2482   $15.25   $15.25   $15.20  
  Purchase #4 $109.91   7.226%   $117.8521   $117.85   $117.85   $117.90  
  Purchase #5 $94.66   10.527%   $104.6249   $104.62   $104.60   $104.60  
  Purchase #6 $192.32   13.296%   $217.8909   $217.89   $217.90   $217.90  
  Purchase #7 $171.26   11.683%   $191.2683   $191.27   $191.25   $191.30  
  7 purchase totals = $967.65       $1,059.2636   $1,059.26   $1,059.25   $1,059.30