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 $38.31   12.828%   $43.2244   $43.22   $43.20   $43.20  
  Purchase #2 $151.76   6.718%   $161.9552   $161.96   $161.95   $162.00  
  Purchase #3 $220.77   7.732%   $237.8399   $237.84   $237.85   $237.80  
  Purchase #4 $58.37   6.199%   $61.9884   $61.99   $62.00   $62.00  
  Purchase #5 $119.63   9.441%   $130.9243   $130.92   $130.90   $130.90  
  Purchase #6 $48.39   13.872%   $55.1027   $55.10   $55.10   $55.10  
  Purchase #7 $47.81   8.809%   $52.0216   $52.02   $52.00   $52.00  
  7 purchase totals = $685.04       $743.0565   $743.05   $743.00   $743.00