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 $245.31   3.183%   $253.1182   $253.12   $253.10   $253.10  
  Purchase #2 $56.63   11.791%   $63.3072   $63.31   $63.30   $63.30  
  Purchase #3 $25.75   10.115%   $28.3546   $28.35   $28.35   $28.40  
  Purchase #4 $216.58   9.252%   $236.618   $236.62   $236.60   $236.60  
  Purchase #5 $130.55   3.510%   $135.1323   $135.13   $135.15   $135.10  
  Purchase #6 $195.37   8.402%   $211.785   $211.79   $211.80   $211.80  
  Purchase #7 $248.89   10.382%   $274.7298   $274.73   $274.75   $274.70  
  7 purchase totals = $1,119.08       $1,203.0451   $1,203.05   $1,203.05   $1,203.00