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 $90.91   11.314%   $101.1956   $101.20   $101.20   $101.20  
  Purchase #2 $238.71   7.372%   $256.3077   $256.31   $256.30   $256.30  
  Purchase #3 $204.69   10.580%   $226.3462   $226.35   $226.35   $226.30  
  Purchase #4 $208.28   6.523%   $221.8661   $221.87   $221.85   $221.90  
  Purchase #5 $108.30   13.849%   $123.2985   $123.30   $123.30   $123.30  
  Purchase #6 $183.48   4.370%   $191.4981   $191.50   $191.50   $191.50  
  Purchase #7 $79.29   4.370%   $82.755   $82.76   $82.75   $82.80  
  7 purchase totals = $1,113.66       $1,203.2672   $1,203.29   $1,203.25   $1,203.30