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 $173.66   13.556%   $197.2013   $197.20   $197.20   $197.20  
  Purchase #2 $180.89   10.825%   $200.4713   $200.47   $200.45   $200.50  
  Purchase #3 $109.46   7.387%   $117.5458   $117.55   $117.55   $117.50  
  Purchase #4 $228.47   8.527%   $247.9516   $247.95   $247.95   $248.00  
  Purchase #5 $5.87   10.648%   $6.495   $6.50   $6.50   $6.50  
  Purchase #6 $37.32   12.253%   $41.8928   $41.89   $41.90   $41.90  
  Purchase #7 $173.77   9.694%   $190.6153   $190.62   $190.60   $190.60  
  7 purchase totals = $909.44       $1,002.1731   $1,002.18   $1,002.15   $1,002.20