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	$52.80	3.123%	$54.4489	$54.45	$54.45	$54.40
Purchase #2	$79.92	11.580%	$89.1747	$89.17	$89.15	$89.20
Purchase #3	$210.61	12.638%	$237.2269	$237.23	$237.25	$237.20
Purchase #4	$235.40	13.257%	$266.607	$266.61	$266.60	$266.60
Purchase #5	$247.68	11.815%	$276.9434	$276.94	$276.95	$276.90
Purchase #6	$36.39	9.683%	$39.9136	$39.91	$39.90	$39.90
Purchase #7	$7.30	8.322%	$7.9075	$7.91	$7.90	$7.90
7 purchase totals =	$870.10		$972.2220	$972.22	$972.20	$972.10