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 $225.74   10.202%   $248.77   $248.77   $248.75   $248.80  
  Purchase #2 $136.63   3.225%   $141.0363   $141.04   $141.05   $141.00  
  Purchase #3 $156.82   5.404%   $165.2946   $165.29   $165.30   $165.30  
  Purchase #4 $218.86   10.401%   $241.6236   $241.62   $241.60   $241.60  
  Purchase #5 $151.69   4.157%   $157.9958   $158.00   $158.00   $158.00  
  Purchase #6 $120.60   3.144%   $124.3917   $124.39   $124.40   $124.40  
  Purchase #7 $155.59   12.137%   $174.474   $174.47   $174.45   $174.50  
  7 purchase totals = $1,165.93       $1,253.5860   $1,253.58   $1,253.55   $1,253.60