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	$92.32	8.705%	$100.3565	$100.36	$100.35	$100.40
Purchase #2	$199.79	6.470%	$212.7164	$212.72	$212.70	$212.70
Purchase #3	$23.29	4.174%	$24.2621	$24.26	$24.25	$24.30
Purchase #4	$242.90	13.599%	$275.932	$275.93	$275.95	$275.90
Purchase #5	$242.59	11.770%	$271.1428	$271.14	$271.15	$271.10
Purchase #6	$33.43	4.154%	$34.8187	$34.82	$34.80	$34.80
Purchase #7	$6.49	12.629%	$7.3096	$7.31	$7.30	$7.30
7 purchase totals =	$840.81		$926.5381	$926.54	$926.50	$926.50