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 $60.93   11.533%   $67.9571   $67.96   $67.95   $68.00  
  Purchase #2 $163.96   8.851%   $178.4721   $178.47   $178.45   $178.50  
  Purchase #3 $132.94   12.151%   $149.0935   $149.09   $149.10   $149.10  
  Purchase #4 $7.28   13.497%   $8.2626   $8.26   $8.25   $8.30  
  Purchase #5 $192.56   8.535%   $208.995   $209.00   $209.00   $209.00  
  Purchase #6 $125.72   10.130%   $138.4554   $138.46   $138.45   $138.50  
  Purchase #7 $91.60   13.457%   $103.9266   $103.93   $103.95   $103.90  
  7 purchase totals = $774.99       $855.1623   $855.17   $855.15   $855.30