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	$90.61	3.283%	$93.5847	$93.58	$93.60	$93.60
Purchase #2	$197.86	8.352%	$214.3853	$214.39	$214.40	$214.40
Purchase #3	$23.63	6.516%	$25.1697	$25.17	$25.15	$25.20
Purchase #4	$137.93	3.857%	$143.25	$143.25	$143.25	$143.30
Purchase #5	$119.57	3.614%	$123.8913	$123.89	$123.90	$123.90
Purchase #6	$43.78	5.245%	$46.0763	$46.08	$46.10	$46.10
Purchase #7	$35.57	4.275%	$37.0906	$37.09	$37.10	$37.10
7 purchase totals =	$648.95		$683.4479	$683.45	$683.50	$683.60