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 $87.43   9.716%   $95.9247   $95.92   $95.90   $95.90  
  Purchase #2 $225.30   4.795%   $236.1031   $236.10   $236.10   $236.10  
  Purchase #3 $184.74   4.525%   $193.0995   $193.10   $193.10   $193.10  
  Purchase #4 $9.83   10.474%   $10.8596   $10.86   $10.85   $10.90  
  Purchase #5 $91.35   4.209%   $95.1949   $95.19   $95.20   $95.20  
  Purchase #6 $50.87   10.360%   $56.1401   $56.14   $56.15   $56.10  
  Purchase #7 $152.60   10.565%   $168.7222   $168.72   $168.70   $168.70  
  7 purchase totals = $802.12       $856.0441   $856.03   $856.00   $856.00