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 $207.68   12.306%   $233.2371   $233.24   $233.25   $233.20  
  Purchase #2 $249.96   12.445%   $281.0675   $281.07   $281.05   $281.10  
  Purchase #3 $117.50   4.689%   $123.0096   $123.01   $123.00   $123.00  
  Purchase #4 $61.43   3.492%   $63.5751   $63.58   $63.60   $63.60  
  Purchase #5 $215.62   8.347%   $233.6178   $233.62   $233.60   $233.60  
  Purchase #6 $205.41   3.844%   $213.306   $213.31   $213.30   $213.30  
  Purchase #7 $154.49   7.159%   $165.5499   $165.55   $165.55   $165.50  
  7 purchase totals = $1,212.09       $1,313.3630   $1,313.38   $1,313.35   $1,313.30