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 $61.63   8.269%   $66.7262   $66.73   $66.75   $66.70  
  Purchase #2 $75.28   3.551%   $77.9532   $77.95   $77.95   $78.00  
  Purchase #3 $207.36   8.873%   $225.7591   $225.76   $225.75   $225.80  
  Purchase #4 $164.34   5.593%   $173.5315   $173.53   $173.55   $173.50  
  Purchase #5 $16.81   5.279%   $17.6974   $17.70   $17.70   $17.70  
  Purchase #6 $221.84   4.198%   $231.1528   $231.15   $231.15   $231.20  
  Purchase #7 $205.77   13.346%   $233.2321   $233.23   $233.25   $233.20  
  7 purchase totals = $953.03       $1,026.0523   $1,026.05   $1,026.10   $1,026.10