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 $61.69   9.747%   $67.7029   $67.70   $67.70   $67.70  
  Purchase #2 $40.99   6.359%   $43.5966   $43.60   $43.60   $43.60  
  Purchase #3 $211.38   12.480%   $237.7602   $237.76   $237.75   $237.80  
  Purchase #4 $172.78   7.686%   $186.0599   $186.06   $186.05   $186.10  
  Purchase #5 $204.63   8.171%   $221.3503   $221.35   $221.35   $221.40  
  Purchase #6 $158.81   6.837%   $169.6678   $169.67   $169.65   $169.70  
  Purchase #7 $23.73   5.130%   $24.9473   $24.95   $24.95   $24.90  
  7 purchase totals = $874.01       $951.0850   $951.09   $951.05   $951.20