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 $56.92   8.805%   $61.9318   $61.93   $61.95   $61.90  
  Purchase #2 $189.73   6.852%   $202.7303   $202.73   $202.75   $202.70  
  Purchase #3 $207.96   12.300%   $233.5391   $233.54   $233.55   $233.50  
  Purchase #4 $181.61   4.749%   $190.2347   $190.23   $190.25   $190.20  
  Purchase #5 $171.71   3.834%   $178.2934   $178.29   $178.30   $178.30  
  Purchase #6 $63.63   9.321%   $69.561   $69.56   $69.55   $69.60  
  Purchase #7 $14.28   8.742%   $15.5284   $15.53   $15.55   $15.50  
  7 purchase totals = $885.84       $951.8187   $951.81   $951.90   $951.70