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 $184.34   6.107%   $195.5976   $195.60   $195.60   $195.60  
  Purchase #2 $155.94   13.223%   $176.5599   $176.56   $176.55   $176.60  
  Purchase #3 $6.85   6.865%   $7.3203   $7.32   $7.30   $7.30  
  Purchase #4 $46.57   8.665%   $50.6053   $50.61   $50.60   $50.60  
  Purchase #5 $127.94   4.819%   $134.1054   $134.11   $134.10   $134.10  
  Purchase #6 $117.65   12.493%   $132.348   $132.35   $132.35   $132.30  
  Purchase #7 $233.70   6.635%   $249.206   $249.21   $249.20   $249.20  
  7 purchase totals = $872.99       $945.7425   $945.76   $945.70   $945.70