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 $208.86   13.114%   $236.2499   $236.25   $236.25   $236.20  
  Purchase #2 $6.68   9.189%   $7.2938   $7.29   $7.30   $7.30  
  Purchase #3 $47.61   5.671%   $50.31   $50.31   $50.30   $50.30  
  Purchase #4 $85.97   3.569%   $89.0383   $89.04   $89.05   $89.00  
  Purchase #5 $216.67   8.295%   $234.6428   $234.64   $234.65   $234.60  
  Purchase #6 $70.67   7.234%   $75.7823   $75.78   $75.80   $75.80  
  Purchase #7 $173.74   4.503%   $181.5635   $181.56   $181.55   $181.60  
  7 purchase totals = $810.20       $874.8806   $874.87   $874.90   $874.80