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	$99.99	11.549%	$111.5378	$111.54	$111.55	$111.50
Purchase #2	$6.27	3.258%	$6.4743	$6.47	$6.45	$6.50
Purchase #3	$79.77	10.587%	$88.2152	$88.22	$88.20	$88.20
Purchase #4	$50.54	7.494%	$54.3275	$54.33	$54.35	$54.30
Purchase #5	$240.91	11.296%	$268.1232	$268.12	$268.10	$268.10
Purchase #6	$93.46	3.185%	$96.4367	$96.44	$96.45	$96.40
Purchase #7	$171.79	4.501%	$179.5223	$179.52	$179.50	$179.50
7 purchase totals =	$742.73		$804.6370	$804.64	$804.60	$804.50