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 $221.62   4.262%   $231.0654   $231.07   $231.05   $231.10  
  Purchase #2 $118.51   4.567%   $123.9224   $123.92   $123.90   $123.90  
  Purchase #3 $100.63   9.167%   $109.8548   $109.85   $109.85   $109.90  
  Purchase #4 $150.75   4.362%   $157.3257   $157.33   $157.35   $157.30  
  Purchase #5 $134.65   6.869%   $143.8991   $143.90   $143.90   $143.90  
  Purchase #6 $240.66   12.396%   $270.4922   $270.49   $270.50   $270.50  
  Purchase #7 $6.91   10.500%   $7.6356   $7.64   $7.65   $7.60  
  7 purchase totals = $973.73       $1,044.1952   $1,044.20   $1,044.20   $1,044.20