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 $233.59   8.332%   $253.0527   $253.05   $253.05   $253.10  
  Purchase #2 $114.75   8.367%   $124.3511   $124.35   $124.35   $124.40  
  Purchase #3 $173.30   4.312%   $180.7727   $180.77   $180.75   $180.80  
  Purchase #4 $20.91   13.594%   $23.7525   $23.75   $23.75   $23.80  
  Purchase #5 $134.25   7.812%   $144.7376   $144.74   $144.75   $144.70  
  Purchase #6 $168.85   9.512%   $184.911   $184.91   $184.90   $184.90  
  Purchase #7 $14.27   4.447%   $14.9046   $14.90   $14.90   $14.90  
  7 purchase totals = $859.92       $926.4822   $926.47   $926.45   $926.60