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 $93.47   11.296%   $104.0284   $104.03   $104.05   $104.00  
  Purchase #2 $133.80   12.626%   $150.6936   $150.69   $150.70   $150.70  
  Purchase #3 $180.41   8.202%   $195.2072   $195.21   $195.20   $195.20  
  Purchase #4 $98.55   5.266%   $103.7396   $103.74   $103.75   $103.70  
  Purchase #5 $210.36   7.526%   $226.1917   $226.19   $226.20   $226.20  
  Purchase #6 $150.59   12.222%   $168.9951   $169.00   $169.00   $169.00  
  Purchase #7 $6.61   8.124%   $7.147   $7.15   $7.15   $7.10  
  7 purchase totals = $873.79       $956.0026   $956.01   $956.05   $955.90