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	$80.34	10.160%	$88.5025	$88.50	$88.50	$88.50
Purchase #2	$165.47	7.663%	$178.15	$178.15	$178.15	$178.20
Purchase #3	$71.78	9.307%	$78.4606	$78.46	$78.45	$78.50
Purchase #4	$96.69	11.184%	$107.5038	$107.50	$107.50	$107.50
Purchase #5	$215.47	10.664%	$238.4477	$238.45	$238.45	$238.40
Purchase #6	$87.80	5.318%	$92.4692	$92.47	$92.45	$92.50
Purchase #7	$65.31	6.444%	$69.5186	$69.52	$69.50	$69.50
7 purchase totals =	$782.86		$853.0524	$853.05	$853.00	$853.10