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 $218.60   6.818%   $233.5041   $233.50   $233.50   $233.50  
  Purchase #2 $160.47   8.616%   $174.2961   $174.30   $174.30   $174.30  
  Purchase #3 $107.27   7.167%   $114.958   $114.96   $114.95   $115.00  
  Purchase #4 $54.69   6.463%   $58.2246   $58.22   $58.20   $58.20  
  Purchase #5 $88.64   10.430%   $97.8852   $97.89   $97.90   $97.90  
  Purchase #6 $15.88   4.228%   $16.5514   $16.55   $16.55   $16.60  
  Purchase #7 $121.84   13.108%   $137.8108   $137.81   $137.80   $137.80  
  7 purchase totals = $767.39       $833.2302   $833.23   $833.20   $833.30