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 $91.44   4.131%   $95.2174   $95.22   $95.20   $95.20  
  Purchase #2 $233.63   4.351%   $243.7952   $243.80   $243.80   $243.80  
  Purchase #3 $183.82   8.380%   $199.2241   $199.22   $199.20   $199.20  
  Purchase #4 $177.37   13.275%   $200.9159   $200.92   $200.90   $200.90  
  Purchase #5 $225.99   10.326%   $249.3257   $249.33   $249.35   $249.30  
  Purchase #6 $173.90   9.608%   $190.6083   $190.61   $190.60   $190.60  
  Purchase #7 $101.87   13.236%   $115.3535   $115.35   $115.35   $115.40  
  7 purchase totals = $1,188.02       $1,294.4401   $1,294.45   $1,294.40   $1,294.40