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	$131.53	5.515%	$138.7839	$138.78	$138.80	$138.80
Purchase #2	$245.41	8.136%	$265.3766	$265.38	$265.40	$265.40
Purchase #3	$173.26	4.276%	$180.6686	$180.67	$180.65	$180.70
Purchase #4	$10.36	12.772%	$11.6832	$11.68	$11.70	$11.70
Purchase #5	$73.43	6.585%	$78.2654	$78.27	$78.25	$78.30
Purchase #6	$127.82	7.315%	$137.17	$137.17	$137.15	$137.20
Purchase #7	$152.77	8.848%	$166.2871	$166.29	$166.30	$166.30
7 purchase totals =	$914.58		$978.2348	$978.24	$978.25	$978.40