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 $241.42   3.459%   $249.7707   $249.77   $249.75   $249.80  
  Purchase #2 $70.37   3.505%   $72.8365   $72.84   $72.85   $72.80  
  Purchase #3 $213.61   3.352%   $220.7702   $220.77   $220.75   $220.80  
  Purchase #4 $202.40   8.251%   $219.1   $219.10   $219.10   $219.10  
  Purchase #5 $74.37   8.729%   $80.8618   $80.86   $80.85   $80.90  
  Purchase #6 $190.39   4.522%   $198.9994   $199.00   $199.00   $199.00  
  Purchase #7 $184.86   12.659%   $208.2614   $208.26   $208.25   $208.30  
  7 purchase totals = $1,177.42       $1,250.6000   $1,250.60   $1,250.55   $1,250.70