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 $62.29   9.597%   $68.268   $68.27   $68.25   $68.30  
  Purchase #2 $89.51   7.775%   $96.4694   $96.47   $96.45   $96.50  
  Purchase #3 $181.97   6.268%   $193.3759   $193.38   $193.40   $193.40  
  Purchase #4 $45.69   5.860%   $48.3674   $48.37   $48.35   $48.40  
  Purchase #5 $47.40   6.403%   $50.435   $50.44   $50.45   $50.40  
  Purchase #6 $192.93   3.419%   $199.5263   $199.53   $199.55   $199.50  
  Purchase #7 $17.79   11.458%   $19.8284   $19.83   $19.85   $19.80  
  7 purchase totals = $637.58       $676.2704   $676.29   $676.30   $676.30