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 $108.44   5.825%   $114.7566   $114.76   $114.75   $114.80  
  Purchase #2 $155.70   6.384%   $165.6399   $165.64   $165.65   $165.60  
  Purchase #3 $68.84   12.312%   $77.3156   $77.32   $77.30   $77.30  
  Purchase #4 $245.45   5.596%   $259.1854   $259.19   $259.20   $259.20  
  Purchase #5 $144.90   3.132%   $149.4383   $149.44   $149.45   $149.40  
  Purchase #6 $236.90   10.738%   $262.3383   $262.34   $262.35   $262.30  
  Purchase #7 $204.50   5.525%   $215.7986   $215.80   $215.80   $215.80  
  7 purchase totals = $1,164.73       $1,244.4727   $1,244.49   $1,244.50   $1,244.40