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	$189.94	13.501%	$215.5838	$215.58	$215.60	$215.60
Purchase #2	$158.85	3.730%	$164.7751	$164.78	$164.80	$164.80
Purchase #3	$85.88	4.438%	$89.6914	$89.69	$89.70	$89.70
Purchase #4	$129.32	9.370%	$141.4373	$141.44	$141.45	$141.40
Purchase #5	$211.64	10.478%	$233.8156	$233.82	$233.80	$233.80
Purchase #6	$206.36	13.301%	$233.8079	$233.81	$233.80	$233.80
Purchase #7	$229.73	11.665%	$256.528	$256.53	$256.55	$256.50
7 purchase totals =	$1,211.72		$1,335.6391	$1,335.65	$1,335.70	$1,335.60