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 $92.36   6.580%   $98.4373   $98.44   $98.45   $98.40  
  Purchase #2 $45.27   5.273%   $47.6571   $47.66   $47.65   $47.70  
  Purchase #3 $58.33   5.369%   $61.4617   $61.46   $61.45   $61.50  
  Purchase #4 $164.77   13.193%   $186.5081   $186.51   $186.50   $186.50  
  Purchase #5 $131.32   8.144%   $142.0147   $142.01   $142.00   $142.00  
  Purchase #6 $120.90   7.247%   $129.6616   $129.66   $129.65   $129.70  
  Purchase #7 $46.85   7.478%   $50.3534   $50.35   $50.35   $50.40  
  7 purchase totals = $659.80       $716.0939   $716.09   $716.05   $716.20