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 $79.91   6.667%   $85.2376   $85.24   $85.25   $85.20  
  Purchase #2 $189.73   5.216%   $199.6263   $199.63   $199.65   $199.60  
  Purchase #3 $162.77   9.830%   $178.7703   $178.77   $178.75   $178.80  
  Purchase #4 $193.71   10.762%   $214.5571   $214.56   $214.55   $214.60  
  Purchase #5 $200.56   7.735%   $216.0733   $216.07   $216.05   $216.10  
  Purchase #6 $22.60   6.656%   $24.1043   $24.10   $24.10   $24.10  
  Purchase #7 $34.63   4.557%   $36.2081   $36.21   $36.20   $36.20  
  7 purchase totals = $883.91       $954.5770   $954.58   $954.55   $954.60