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 $38.52   13.611%   $43.763   $43.76   $43.75   $43.80  
  Purchase #2 $217.91   9.522%   $238.6594   $238.66   $238.65   $238.70  
  Purchase #3 $48.75   9.672%   $53.4651   $53.47   $53.45   $53.50  
  Purchase #4 $106.67   13.181%   $120.7302   $120.73   $120.75   $120.70  
  Purchase #5 $11.54   4.376%   $12.045   $12.05   $12.05   $12.00  
  Purchase #6 $174.85   4.415%   $182.5696   $182.57   $182.55   $182.60  
  Purchase #7 $57.73   8.491%   $62.6319   $62.63   $62.65   $62.60  
  7 purchase totals = $655.97       $713.8642   $713.87   $713.85   $713.90