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 $69.95   9.514%   $76.605   $76.61   $76.60   $76.60  
  Purchase #2 $205.89   9.213%   $224.8586   $224.86   $224.85   $224.90  
  Purchase #3 $234.93   10.634%   $259.9125   $259.91   $259.90   $259.90  
  Purchase #4 $246.37   12.437%   $277.011   $277.01   $277.00   $277.00  
  Purchase #5 $146.57   4.775%   $153.5687   $153.57   $153.55   $153.60  
  Purchase #6 $102.85   12.580%   $115.7885   $115.79   $115.80   $115.80  
  Purchase #7 $109.44   13.128%   $123.8073   $123.81   $123.80   $123.80  
  7 purchase totals = $1,116.00       $1,231.5516   $1,231.56   $1,231.50   $1,231.60