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 $56.73   12.645%   $63.9035   $63.90   $63.90   $63.90  
  Purchase #2 $195.51   6.824%   $208.8516   $208.85   $208.85   $208.90  
  Purchase #3 $216.39   9.403%   $236.7372   $236.74   $236.75   $236.70  
  Purchase #4 $234.47   10.425%   $258.9135   $258.91   $258.90   $258.90  
  Purchase #5 $152.57   10.316%   $168.3091   $168.31   $168.30   $168.30  
  Purchase #6 $182.54   9.514%   $199.9069   $199.91   $199.90   $199.90  
  Purchase #7 $209.87   7.792%   $226.2231   $226.22   $226.20   $226.20  
  7 purchase totals = $1,248.08       $1,362.8449   $1,362.84   $1,362.80   $1,362.80