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 $214.60   8.667%   $233.1994   $233.20   $233.20   $233.20  
  Purchase #2 $188.92   7.131%   $202.3919   $202.39   $202.40   $202.40  
  Purchase #3 $15.96   6.474%   $16.9933   $16.99   $17.00   $17.00  
  Purchase #4 $243.60   12.508%   $274.0695   $274.07   $274.05   $274.10  
  Purchase #5 $58.45   11.296%   $65.0525   $65.05   $65.05   $65.10  
  Purchase #6 $45.36   3.673%   $47.0261   $47.03   $47.05   $47.00  
  Purchase #7 $111.48   6.400%   $118.6147   $118.61   $118.60   $118.60  
  7 purchase totals = $878.37       $957.3474   $957.34   $957.35   $957.40