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 $235.82   3.546%   $244.1822   $244.18   $244.20   $244.20  
  Purchase #2 $241.76   5.425%   $254.8755   $254.88   $254.90   $254.90  
  Purchase #3 $157.48   6.455%   $167.6453   $167.65   $167.65   $167.60  
  Purchase #4 $151.29   11.229%   $168.2784   $168.28   $168.30   $168.30  
  Purchase #5 $250.61   6.483%   $266.857   $266.86   $266.85   $266.90  
  Purchase #6 $21.82   6.699%   $23.2817   $23.28   $23.30   $23.30  
  Purchase #7 $243.90   4.828%   $255.6755   $255.68   $255.70   $255.70  
  7 purchase totals = $1,302.68       $1,380.7956   $1,380.81   $1,380.90   $1,380.90