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 $224.38   11.213%   $249.5397   $249.54   $249.55   $249.50  
  Purchase #2 $50.89   7.247%   $54.578   $54.58   $54.60   $54.60  
  Purchase #3 $211.32   4.464%   $220.7533   $220.75   $220.75   $220.80  
  Purchase #4 $126.91   9.697%   $139.2165   $139.22   $139.20   $139.20  
  Purchase #5 $214.45   12.514%   $241.2863   $241.29   $241.30   $241.30  
  Purchase #6 $38.97   3.259%   $40.24   $40.24   $40.25   $40.20  
  Purchase #7 $97.55   9.370%   $106.6904   $106.69   $106.70   $106.70  
  7 purchase totals = $964.47       $1,052.3042   $1,052.31   $1,052.35   $1,052.30