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 $204.50   10.720%   $226.4224   $226.42   $226.40   $226.40  
  Purchase #2 $123.27   11.842%   $137.8676   $137.87   $137.85   $137.90  
  Purchase #3 $151.35   11.255%   $168.3844   $168.38   $168.40   $168.40  
  Purchase #4 $188.61   3.787%   $195.7527   $195.75   $195.75   $195.80  
  Purchase #5 $245.87   5.663%   $259.7936   $259.79   $259.80   $259.80  
  Purchase #6 $5.49   6.515%   $5.8477   $5.85   $5.85   $5.80  
  Purchase #7 $26.44   11.689%   $29.5306   $29.53   $29.55   $29.50  
  7 purchase totals = $945.53       $1,023.5990   $1,023.59   $1,023.60   $1,023.60