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 $192.61   4.709%   $201.68   $201.68   $201.70   $201.70  
  Purchase #2 $12.91   13.383%   $14.6377   $14.64   $14.65   $14.60  
  Purchase #3 $61.81   12.766%   $69.7007   $69.70   $69.70   $69.70  
  Purchase #4 $125.52   10.673%   $138.9167   $138.92   $138.90   $138.90  
  Purchase #5 $31.44   12.604%   $35.4027   $35.40   $35.40   $35.40  
  Purchase #6 $108.30   8.723%   $117.747   $117.75   $117.75   $117.70  
  Purchase #7 $73.89   5.414%   $77.8904   $77.89   $77.90   $77.90  
  7 purchase totals = $606.48       $655.9752   $655.98   $656.00   $655.90