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 $34.86   10.521%   $38.5276   $38.53   $38.55   $38.50  
  Purchase #2 $178.46   3.234%   $184.2314   $184.23   $184.25   $184.20  
  Purchase #3 $196.27   4.381%   $204.8686   $204.87   $204.85   $204.90  
  Purchase #4 $222.85   9.804%   $244.6982   $244.70   $244.70   $244.70  
  Purchase #5 $238.94   9.638%   $261.969   $261.97   $261.95   $262.00  
  Purchase #6 $207.32   3.396%   $214.3606   $214.36   $214.35   $214.40  
  Purchase #7 $73.59   5.335%   $77.516   $77.52   $77.50   $77.50  
  7 purchase totals = $1,152.29       $1,226.1714   $1,226.18   $1,226.15   $1,226.20