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 $183.49   5.182%   $192.9985   $193.00   $193.00   $193.00  
  Purchase #2 $105.41   5.853%   $111.5796   $111.58   $111.60   $111.60  
  Purchase #3 $246.30   8.195%   $266.4843   $266.48   $266.50   $266.50  
  Purchase #4 $190.47   12.335%   $213.9645   $213.96   $213.95   $214.00  
  Purchase #5 $233.46   9.390%   $255.3819   $255.38   $255.40   $255.40  
  Purchase #6 $163.46   3.183%   $168.6629   $168.66   $168.65   $168.70  
  Purchase #7 $120.54   3.529%   $124.7939   $124.79   $124.80   $124.80  
  7 purchase totals = $1,243.13       $1,333.8656   $1,333.85   $1,333.90   $1,334.00