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 $66.82   10.793%   $74.0319   $74.03   $74.05   $74.00  
  Purchase #2 $35.46   6.739%   $37.8496   $37.85   $37.85   $37.80  
  Purchase #3 $158.27   6.871%   $169.1447   $169.14   $169.15   $169.10  
  Purchase #4 $109.68   7.360%   $117.7524   $117.75   $117.75   $117.80  
  Purchase #5 $161.61   6.873%   $172.7175   $172.72   $172.70   $172.70  
  Purchase #6 $207.56   6.859%   $221.7965   $221.80   $221.80   $221.80  
  Purchase #7 $62.63   12.411%   $70.403   $70.40   $70.40   $70.40  
  7 purchase totals = $802.03       $863.6956   $863.69   $863.70   $863.60