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 $235.75   10.802%   $261.2157   $261.22   $261.20   $261.20  
  Purchase #2 $101.98   6.487%   $108.5954   $108.60   $108.60   $108.60  
  Purchase #3 $80.26   4.172%   $83.6084   $83.61   $83.60   $83.60  
  Purchase #4 $211.38   7.273%   $226.7537   $226.75   $226.75   $226.80  
  Purchase #5 $137.93   11.715%   $154.0885   $154.09   $154.10   $154.10  
  Purchase #6 $178.26   9.515%   $195.2214   $195.22   $195.20   $195.20  
  Purchase #7 $107.28   6.649%   $114.413   $114.41   $114.40   $114.40  
  7 purchase totals = $1,052.84       $1,143.8961   $1,143.90   $1,143.85   $1,143.90