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 $114.31   10.778%   $126.6303   $126.63   $126.65   $126.60  
  Purchase #2 $216.31   7.857%   $233.3055   $233.31   $233.30   $233.30  
  Purchase #3 $135.48   7.739%   $145.9648   $145.96   $145.95   $146.00  
  Purchase #4 $40.37   6.343%   $42.9307   $42.93   $42.95   $42.90  
  Purchase #5 $71.49   7.656%   $76.9633   $76.96   $76.95   $77.00  
  Purchase #6 $153.70   4.423%   $160.4982   $160.50   $160.50   $160.50  
  Purchase #7 $125.72   12.714%   $141.704   $141.70   $141.70   $141.70  
  7 purchase totals = $857.38       $927.9968   $927.99   $928.00   $928.00