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 $107.46   6.286%   $114.2149   $114.21   $114.20   $114.20  
  Purchase #2 $97.89   4.481%   $102.2765   $102.28   $102.30   $102.30  
  Purchase #3 $24.49   13.143%   $27.7087   $27.71   $27.70   $27.70  
  Purchase #4 $238.77   10.528%   $263.9077   $263.91   $263.90   $263.90  
  Purchase #5 $165.85   9.802%   $182.1066   $182.11   $182.10   $182.10  
  Purchase #6 $34.35   7.494%   $36.9242   $36.92   $36.90   $36.90  
  Purchase #7 $62.74   9.189%   $68.5052   $68.51   $68.50   $68.50  
  7 purchase totals = $731.55       $795.6438   $795.65   $795.60   $795.60