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	$64.77	12.414%	$72.8105	$72.81	$72.80	$72.80
Purchase #2	$81.25	10.751%	$89.9852	$89.99	$90.00	$90.00
Purchase #3	$231.90	5.747%	$245.2273	$245.23	$245.25	$245.20
Purchase #4	$83.61	6.554%	$89.0898	$89.09	$89.10	$89.10
Purchase #5	$219.68	12.496%	$247.1312	$247.13	$247.15	$247.10
Purchase #6	$205.52	11.612%	$229.385	$229.39	$229.40	$229.40
Purchase #7	$158.28	7.322%	$169.8693	$169.87	$169.85	$169.90
7 purchase totals =	$1,045.01		$1,143.4983	$1,143.51	$1,143.55	$1,143.50