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 $216.38   11.574%   $241.4238   $241.42   $241.40   $241.40  
  Purchase #2 $228.27   11.141%   $253.7016   $253.70   $253.70   $253.70  
  Purchase #3 $74.45   11.141%   $82.7445   $82.74   $82.75   $82.70  
  Purchase #4 $196.73   10.533%   $217.4516   $217.45   $217.45   $217.50  
  Purchase #5 $81.62   6.472%   $86.9024   $86.90   $86.90   $86.90  
  Purchase #6 $75.52   6.186%   $80.1917   $80.19   $80.20   $80.20  
  Purchase #7 $9.88   3.114%   $10.1877   $10.19   $10.20   $10.20  
  7 purchase totals = $882.85       $972.6033   $972.59   $972.60   $972.60