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	$104.62	3.174%	$107.9406	$107.94	$107.95	$107.90
Purchase #2	$66.82	8.758%	$72.6721	$72.67	$72.65	$72.70
Purchase #3	$89.61	10.740%	$99.2341	$99.23	$99.25	$99.20
Purchase #4	$115.54	13.594%	$131.2465	$131.25	$131.25	$131.20
Purchase #5	$18.63	3.620%	$19.3044	$19.30	$19.30	$19.30
Purchase #6	$171.70	11.586%	$191.5932	$191.59	$191.60	$191.60
Purchase #7	$22.58	13.805%	$25.6972	$25.70	$25.70	$25.70
7 purchase totals =	$589.50		$647.6881	$647.68	$647.70	$647.60