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	$139.85	13.549%	$158.7983	$158.80	$158.80	$158.80
Purchase #2	$244.99	7.633%	$263.6901	$263.69	$263.70	$263.70
Purchase #3	$38.82	11.558%	$43.3068	$43.31	$43.30	$43.30
Purchase #4	$91.85	10.772%	$101.7441	$101.74	$101.75	$101.70
Purchase #5	$89.93	10.652%	$99.5093	$99.51	$99.50	$99.50
Purchase #6	$231.95	6.598%	$247.2541	$247.25	$247.25	$247.30
Purchase #7	$74.44	12.193%	$83.5165	$83.52	$83.50	$83.50
7 purchase totals =	$911.83		$997.8192	$997.82	$997.80	$997.80