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 $195.55   6.842%   $208.9295   $208.93   $208.95   $208.90  
  Purchase #2 $179.69   10.130%   $197.8926   $197.89   $197.90   $197.90  
  Purchase #3 $158.26   6.107%   $167.9249   $167.92   $167.90   $167.90  
  Purchase #4 $30.73   4.713%   $32.1783   $32.18   $32.20   $32.20  
  Purchase #5 $242.37   10.770%   $268.4732   $268.47   $268.45   $268.50  
  Purchase #6 $124.92   7.738%   $134.5863   $134.59   $134.60   $134.60  
  Purchase #7 $59.28   6.346%   $63.0419   $63.04   $63.05   $63.00  
  7 purchase totals = $990.80       $1,073.0267   $1,073.02   $1,073.05   $1,073.00