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 $53.97   3.783%   $56.0117   $56.01   $56.00   $56.00  
  Purchase #2 $13.68   3.675%   $14.1827   $14.18   $14.20   $14.20  
  Purchase #3 $231.65   5.263%   $243.8417   $243.84   $243.85   $243.80  
  Purchase #4 $164.41   12.451%   $184.8807   $184.88   $184.90   $184.90  
  Purchase #5 $94.83   4.321%   $98.9276   $98.93   $98.95   $98.90  
  Purchase #6 $112.67   8.249%   $121.9641   $121.96   $121.95   $122.00  
  Purchase #7 $213.42   13.526%   $242.2872   $242.29   $242.30   $242.30  
  7 purchase totals = $884.63       $962.0957   $962.09   $962.15   $962.10