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 $104.41   13.211%   $118.2036   $118.20   $118.20   $118.20  
  Purchase #2 $11.57   9.461%   $12.6646   $12.66   $12.65   $12.70  
  Purchase #3 $11.48   9.580%   $12.5798   $12.58   $12.60   $12.60  
  Purchase #4 $91.50   6.640%   $97.5756   $97.58   $97.60   $97.60  
  Purchase #5 $56.63   8.569%   $61.4826   $61.48   $61.50   $61.50  
  Purchase #6 $225.92   6.581%   $240.7878   $240.79   $240.80   $240.80  
  Purchase #7 $202.62   6.398%   $215.5836   $215.58   $215.60   $215.60  
  7 purchase totals = $704.13       $758.8776   $758.87   $758.95   $759.00