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	$153.39	11.789%	$171.4731	$171.47	$171.45	$171.50
Purchase #2	$72.63	6.813%	$77.5783	$77.58	$77.60	$77.60
Purchase #3	$65.33	3.780%	$67.7995	$67.80	$67.80	$67.80
Purchase #4	$116.75	9.580%	$127.9347	$127.93	$127.95	$127.90
Purchase #5	$198.45	8.683%	$215.6814	$215.68	$215.70	$215.70
Purchase #6	$19.33	9.550%	$21.176	$21.18	$21.20	$21.20
Purchase #7	$148.52	12.478%	$167.0523	$167.05	$167.05	$167.10
7 purchase totals =	$774.40		$848.6953	$848.69	$848.75	$848.80