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 $28.48   7.233%   $30.54   $30.54   $30.55   $30.50  
  Purchase #2 $108.73   6.216%   $115.4887   $115.49   $115.50   $115.50  
  Purchase #3 $162.91   3.178%   $168.0873   $168.09   $168.10   $168.10  
  Purchase #4 $119.30   13.592%   $135.5153   $135.52   $135.50   $135.50  
  Purchase #5 $164.30   5.109%   $172.6941   $172.69   $172.70   $172.70  
  Purchase #6 $51.84   5.404%   $54.6414   $54.64   $54.65   $54.60  
  Purchase #7 $49.48   4.605%   $51.7586   $51.76   $51.75   $51.80  
  7 purchase totals = $685.04       $728.7254   $728.73   $728.75   $728.70