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	$138.52	12.254%	$155.4942	$155.49	$155.50	$155.50
Purchase #2	$222.96	9.663%	$244.5046	$244.50	$244.50	$244.50
Purchase #3	$249.59	5.631%	$263.6444	$263.64	$263.65	$263.60
Purchase #4	$223.33	8.364%	$242.0093	$242.01	$242.00	$242.00
Purchase #5	$241.39	5.865%	$255.5475	$255.55	$255.55	$255.50
Purchase #6	$29.92	11.813%	$33.4544	$33.45	$33.45	$33.50
Purchase #7	$94.55	4.284%	$98.6005	$98.60	$98.60	$98.60
7 purchase totals =	$1,200.26		$1,293.2549	$1,293.24	$1,293.25	$1,293.20