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 $51.72   13.372%   $58.636   $58.64   $58.65   $58.60  
  Purchase #2 $242.51   10.855%   $268.8345   $268.83   $268.85   $268.80  
  Purchase #3 $197.86   4.177%   $206.1246   $206.12   $206.10   $206.10  
  Purchase #4 $134.67   4.562%   $140.8136   $140.81   $140.80   $140.80  
  Purchase #5 $205.36   4.813%   $215.244   $215.24   $215.25   $215.20  
  Purchase #6 $172.70   11.123%   $191.9094   $191.91   $191.90   $191.90  
  Purchase #7 $214.74   3.569%   $222.4041   $222.40   $222.40   $222.40  
  7 purchase totals = $1,219.56       $1,303.9662   $1,303.95   $1,303.95   $1,303.80