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 $194.59   7.548%   $209.2777   $209.28   $209.30   $209.30  
  Purchase #2 $21.77   8.510%   $23.6226   $23.62   $23.60   $23.60  
  Purchase #3 $195.63   5.233%   $205.8673   $205.87   $205.85   $205.90  
  Purchase #4 $91.83   5.314%   $96.7098   $96.71   $96.70   $96.70  
  Purchase #5 $249.45   6.849%   $266.5348   $266.53   $266.55   $266.50  
  Purchase #6 $147.58   5.557%   $155.781   $155.78   $155.80   $155.80  
  Purchase #7 $55.44   11.203%   $61.6509   $61.65   $61.65   $61.70  
  7 purchase totals = $956.29       $1,019.4441   $1,019.44   $1,019.45   $1,019.50