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	$18.44	12.776%	$20.7959	$20.80	$20.80	$20.80
Purchase #2	$48.93	7.588%	$52.6428	$52.64	$52.65	$52.60
Purchase #3	$143.78	5.824%	$152.1537	$152.15	$152.15	$152.20
Purchase #4	$230.91	12.418%	$259.5844	$259.58	$259.60	$259.60
Purchase #5	$139.37	3.451%	$144.1797	$144.18	$144.20	$144.20
Purchase #6	$82.99	8.199%	$89.7944	$89.79	$89.80	$89.80
Purchase #7	$235.47	12.230%	$264.268	$264.27	$264.25	$264.30
7 purchase totals =	$899.89		$983.4189	$983.41	$983.45	$983.50