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 $98.81   3.115%   $101.8879   $101.89   $101.90   $101.90  
  Purchase #2 $30.69   12.745%   $34.6014   $34.60   $34.60   $34.60  
  Purchase #3 $61.42   7.725%   $66.1647   $66.16   $66.15   $66.20  
  Purchase #4 $96.57   13.233%   $109.3491   $109.35   $109.35   $109.30  
  Purchase #5 $112.92   7.465%   $121.3495   $121.35   $121.35   $121.30  
  Purchase #6 $208.89   3.697%   $216.6127   $216.61   $216.60   $216.60  
  Purchase #7 $100.49   12.467%   $113.0181   $113.02   $113.00   $113.00  
  7 purchase totals = $709.79       $762.9834   $762.98   $762.95   $762.90