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	$249.61	7.543%	$268.4381	$268.44	$268.45	$268.40
Purchase #2	$193.68	13.271%	$219.3833	$219.38	$219.40	$219.40
Purchase #3	$71.72	10.475%	$79.2327	$79.23	$79.25	$79.20
Purchase #4	$56.81	7.472%	$61.0548	$61.05	$61.05	$61.10
Purchase #5	$43.77	13.283%	$49.584	$49.58	$49.60	$49.60
Purchase #6	$200.73	4.410%	$209.5822	$209.58	$209.60	$209.60
Purchase #7	$174.93	12.514%	$196.8207	$196.82	$196.80	$196.80
7 purchase totals =	$991.25		$1,084.0958	$1,084.08	$1,084.15	$1,084.10