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	$46.53	11.309%	$51.7921	$51.79	$51.80	$51.80
Purchase #2	$79.88	13.752%	$90.8651	$90.87	$90.85	$90.90
Purchase #3	$25.31	8.500%	$27.4614	$27.46	$27.45	$27.50
Purchase #4	$53.81	3.646%	$55.7719	$55.77	$55.75	$55.80
Purchase #5	$57.88	3.807%	$60.0835	$60.08	$60.10	$60.10
Purchase #6	$118.50	11.388%	$131.9948	$131.99	$132.00	$132.00
Purchase #7	$122.63	3.662%	$127.1207	$127.12	$127.10	$127.10
7 purchase totals =	$504.54		$545.0895	$545.08	$545.05	$545.20