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 $131.77   10.323%   $145.3726   $145.37   $145.35   $145.40  
  Purchase #2 $233.90   11.521%   $260.8476   $260.85   $260.85   $260.80  
  Purchase #3 $143.60   7.202%   $153.9421   $153.94   $153.95   $153.90  
  Purchase #4 $214.98   9.834%   $236.1211   $236.12   $236.10   $236.10  
  Purchase #5 $185.27   4.264%   $193.1699   $193.17   $193.15   $193.20  
  Purchase #6 $200.88   8.523%   $218.001   $218.00   $218.00   $218.00  
  Purchase #7 $72.70   7.541%   $78.1823   $78.18   $78.20   $78.20  
  7 purchase totals = $1,183.10       $1,285.6366   $1,285.63   $1,285.60   $1,285.60