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 $202.25   3.170%   $208.6613   $208.66   $208.65   $208.70  
  Purchase #2 $211.55   7.460%   $227.3316   $227.33   $227.35   $227.30  
  Purchase #3 $147.67   10.707%   $163.481   $163.48   $163.50   $163.50  
  Purchase #4 $240.98   5.111%   $253.2965   $253.30   $253.30   $253.30  
  Purchase #5 $151.83   10.398%   $167.6173   $167.62   $167.60   $167.60  
  Purchase #6 $235.51   11.496%   $262.5842   $262.58   $262.60   $262.60  
  Purchase #7 $193.71   11.369%   $215.7329   $215.73   $215.75   $215.70  
  7 purchase totals = $1,383.50       $1,498.7048   $1,498.70   $1,498.75   $1,498.70