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 $92.86   12.816%   $104.7609   $104.76   $104.75   $104.80  
  Purchase #2 $118.39   6.376%   $125.9385   $125.94   $125.95   $125.90  
  Purchase #3 $30.62   11.861%   $34.2518   $34.25   $34.25   $34.30  
  Purchase #4 $75.96   5.147%   $79.8697   $79.87   $79.85   $79.90  
  Purchase #5 $57.66   5.804%   $61.0066   $61.01   $61.00   $61.00  
  Purchase #6 $53.38   3.774%   $55.3946   $55.39   $55.40   $55.40  
  Purchase #7 $221.47   9.535%   $242.5872   $242.59   $242.60   $242.60  
  7 purchase totals = $650.34       $703.8093   $703.81   $703.80   $703.90