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 $100.47   4.138%   $104.6274   $104.63   $104.65   $104.60  
  Purchase #2 $182.34   3.798%   $189.2653   $189.27   $189.25   $189.30  
  Purchase #3 $108.91   3.699%   $112.9386   $112.94   $112.95   $112.90  
  Purchase #4 $72.94   12.685%   $82.1924   $82.19   $82.20   $82.20  
  Purchase #5 $83.67   7.249%   $89.7352   $89.74   $89.75   $89.70  
  Purchase #6 $83.52   5.592%   $88.1904   $88.19   $88.20   $88.20  
  Purchase #7 $68.88   11.769%   $76.9865   $76.99   $77.00   $77.00  
  7 purchase totals = $700.73       $743.9358   $743.95   $744.00   $743.90