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 $71.71   6.291%   $76.2213   $76.22   $76.20   $76.20  
  Purchase #2 $22.36   6.694%   $23.8568   $23.86   $23.85   $23.90  
  Purchase #3 $82.96   5.839%   $87.804   $87.80   $87.80   $87.80  
  Purchase #4 $95.65   10.469%   $105.6636   $105.66   $105.65   $105.70  
  Purchase #5 $95.94   11.189%   $106.6747   $106.67   $106.65   $106.70  
  Purchase #6 $87.78   3.539%   $90.8865   $90.89   $90.90   $90.90  
  Purchase #7 $223.28   3.763%   $231.682   $231.68   $231.70   $231.70  
  7 purchase totals = $679.68       $722.7889   $722.78   $722.75   $722.90