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 $239.39   8.624%   $260.035   $260.04   $260.05   $260.00  
  Purchase #2 $187.43   4.495%   $195.855   $195.86   $195.85   $195.90  
  Purchase #3 $243.86   12.678%   $274.7766   $274.78   $274.80   $274.80  
  Purchase #4 $218.39   8.325%   $236.571   $236.57   $236.55   $236.60  
  Purchase #5 $179.39   8.722%   $195.0364   $195.04   $195.05   $195.00  
  Purchase #6 $178.34   10.728%   $197.4723   $197.47   $197.45   $197.50  
  Purchase #7 $32.67   8.764%   $35.5332   $35.53   $35.55   $35.50  
  7 purchase totals = $1,279.47       $1,395.2795   $1,395.29   $1,395.30   $1,395.30