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 $56.76   6.558%   $60.4823   $60.48   $60.50   $60.50  
  Purchase #2 $211.85   10.354%   $233.7849   $233.78   $233.80   $233.80  
  Purchase #3 $82.92   12.276%   $93.0993   $93.10   $93.10   $93.10  
  Purchase #4 $9.71   9.794%   $10.661   $10.66   $10.65   $10.70  
  Purchase #5 $125.85   13.576%   $142.9354   $142.94   $142.95   $142.90  
  Purchase #6 $56.73   7.367%   $60.9093   $60.91   $60.90   $60.90  
  Purchase #7 $48.25   13.671%   $54.8463   $54.85   $54.85   $54.80  
  7 purchase totals = $592.07       $656.7185   $656.72   $656.75   $656.70