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	$41.63	4.683%	$43.5795	$43.58	$43.60	$43.60
Purchase #2	$40.64	7.105%	$43.5275	$43.53	$43.55	$43.50
Purchase #3	$55.54	6.231%	$59.0007	$59.00	$59.00	$59.00
Purchase #4	$132.54	8.327%	$143.5766	$143.58	$143.60	$143.60
Purchase #5	$56.44	6.494%	$60.1052	$60.11	$60.10	$60.10
Purchase #6	$156.45	7.253%	$167.7973	$167.80	$167.80	$167.80
Purchase #7	$112.58	7.402%	$120.9132	$120.91	$120.90	$120.90
7 purchase totals =	$595.82		$638.5000	$638.51	$638.55	$638.50