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 $213.39   10.826%   $236.4916   $236.49   $236.50   $236.50  
  Purchase #2 $189.89   7.786%   $204.6748   $204.67   $204.65   $204.70  
  Purchase #3 $74.64   13.343%   $84.5992   $84.60   $84.60   $84.60  
  Purchase #4 $241.68   3.424%   $249.9551   $249.96   $249.95   $250.00  
  Purchase #5 $101.87   7.349%   $109.3564   $109.36   $109.35   $109.40  
  Purchase #6 $185.32   3.466%   $191.7432   $191.74   $191.75   $191.70  
  Purchase #7 $57.68   4.727%   $60.4065   $60.41   $60.40   $60.40  
  7 purchase totals = $1,064.47       $1,137.2268   $1,137.23   $1,137.20   $1,137.30