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 $223.48   11.682%   $249.5869   $249.59   $249.60   $249.60  
  Purchase #2 $218.85   12.749%   $246.7512   $246.75   $246.75   $246.80  
  Purchase #3 $58.47   12.868%   $65.9939   $65.99   $66.00   $66.00  
  Purchase #4 $149.84   4.436%   $156.4869   $156.49   $156.50   $156.50  
  Purchase #5 $95.31   5.195%   $100.2614   $100.26   $100.25   $100.30  
  Purchase #6 $248.61   12.238%   $279.0349   $279.03   $279.05   $279.00  
  Purchase #7 $14.70   10.472%   $16.2394   $16.24   $16.25   $16.20  
  7 purchase totals = $1,009.26       $1,114.3546   $1,114.35   $1,114.40   $1,114.40