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 $244.26   6.102%   $259.1647   $259.16   $259.15   $259.20  
  Purchase #2 $56.48   13.600%   $64.1613   $64.16   $64.15   $64.20  
  Purchase #3 $164.90   7.759%   $177.6946   $177.69   $177.70   $177.70  
  Purchase #4 $167.33   8.348%   $181.2987   $181.30   $181.30   $181.30  
  Purchase #5 $184.81   12.711%   $208.3012   $208.30   $208.30   $208.30  
  Purchase #6 $35.67   3.798%   $37.0247   $37.02   $37.00   $37.00  
  Purchase #7 $60.39   10.784%   $66.9025   $66.90   $66.90   $66.90  
  7 purchase totals = $913.84       $994.5477   $994.53   $994.50   $994.60