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 $244.69   5.698%   $258.6324   $258.63   $258.65   $258.60  
  Purchase #2 $66.58   7.199%   $71.3731   $71.37   $71.35   $71.40  
  Purchase #3 $64.40   6.510%   $68.5924   $68.59   $68.60   $68.60  
  Purchase #4 $227.42   8.132%   $245.9138   $245.91   $245.90   $245.90  
  Purchase #5 $209.45   7.307%   $224.7545   $224.75   $224.75   $224.80  
  Purchase #6 $197.42   13.217%   $223.513   $223.51   $223.50   $223.50  
  Purchase #7 $240.63   9.109%   $262.549   $262.55   $262.55   $262.50  
  7 purchase totals = $1,250.59       $1,355.3282   $1,355.31   $1,355.30   $1,355.30