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 $204.80   9.284%   $223.8136   $223.81   $223.80   $223.80  
  Purchase #2 $177.80   10.139%   $195.8271   $195.83   $195.85   $195.80  
  Purchase #3 $21.98   9.236%   $24.0101   $24.01   $24.00   $24.00  
  Purchase #4 $50.57   6.475%   $53.8444   $53.84   $53.85   $53.80  
  Purchase #5 $185.63   9.854%   $203.922   $203.92   $203.90   $203.90  
  Purchase #6 $179.78   9.160%   $196.2478   $196.25   $196.25   $196.20  
  Purchase #7 $250.75   11.247%   $278.9519   $278.95   $278.95   $279.00  
  7 purchase totals = $1,071.31       $1,176.6169   $1,176.61   $1,176.60   $1,176.50