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 $119.53   10.658%   $132.2695   $132.27   $132.25   $132.30  
  Purchase #2 $93.93   9.252%   $102.6204   $102.62   $102.60   $102.60  
  Purchase #3 $18.94   7.710%   $20.4003   $20.40   $20.40   $20.40  
  Purchase #4 $169.93   9.687%   $186.3911   $186.39   $186.40   $186.40  
  Purchase #5 $36.90   6.334%   $39.2372   $39.24   $39.25   $39.20  
  Purchase #6 $151.42   13.874%   $172.428   $172.43   $172.45   $172.40  
  Purchase #7 $23.44   4.138%   $24.4099   $24.41   $24.40   $24.40  
  7 purchase totals = $614.09       $677.7564   $677.76   $677.75   $677.70