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 $60.92   12.301%   $68.4138   $68.41   $68.40   $68.40  
  Purchase #2 $175.69   12.672%   $197.9534   $197.95   $197.95   $198.00  
  Purchase #3 $200.81   10.296%   $221.4854   $221.49   $221.50   $221.50  
  Purchase #4 $113.52   12.504%   $127.7145   $127.71   $127.70   $127.70  
  Purchase #5 $199.95   4.635%   $209.2177   $209.22   $209.20   $209.20  
  Purchase #6 $43.86   8.141%   $47.4306   $47.43   $47.45   $47.40  
  Purchase #7 $101.74   4.232%   $106.0456   $106.05   $106.05   $106.00  
  7 purchase totals = $896.49       $978.2610   $978.26   $978.25   $978.20