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 $50.63   6.467%   $53.9042   $53.90   $53.90   $53.90  
  Purchase #2 $205.84   13.549%   $233.7293   $233.73   $233.75   $233.70  
  Purchase #3 $175.92   13.259%   $199.2452   $199.25   $199.25   $199.20  
  Purchase #4 $152.39   6.427%   $162.1841   $162.18   $162.20   $162.20  
  Purchase #5 $150.50   3.303%   $155.471   $155.47   $155.45   $155.50  
  Purchase #6 $27.77   5.441%   $29.281   $29.28   $29.30   $29.30  
  Purchase #7 $219.91   7.400%   $236.1833   $236.18   $236.20   $236.20  
  7 purchase totals = $982.96       $1,069.9981   $1,069.99   $1,070.05   $1,070.00