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 $182.64   4.509%   $190.8752   $190.88   $190.90   $190.90  
  Purchase #2 $82.30   10.650%   $91.065   $91.07   $91.05   $91.10  
  Purchase #3 $168.38   6.665%   $179.6025   $179.60   $179.60   $179.60  
  Purchase #4 $112.63   10.472%   $124.4246   $124.42   $124.40   $124.40  
  Purchase #5 $137.57   7.417%   $147.7736   $147.77   $147.75   $147.80  
  Purchase #6 $220.76   3.169%   $227.7559   $227.76   $227.75   $227.80  
  Purchase #7 $182.46   8.120%   $197.2758   $197.28   $197.30   $197.30  
  7 purchase totals = $1,086.74       $1,158.7726   $1,158.78   $1,158.75   $1,158.90