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	$212.73	13.111%	$240.621	$240.62	$240.60	$240.60
Purchase #2	$243.74	5.174%	$256.3511	$256.35	$256.35	$256.40
Purchase #3	$30.88	4.408%	$32.2412	$32.24	$32.25	$32.20
Purchase #4	$225.40	3.468%	$233.2169	$233.22	$233.20	$233.20
Purchase #5	$128.37	12.109%	$143.9143	$143.91	$143.90	$143.90
Purchase #6	$125.56	5.621%	$132.6177	$132.62	$132.60	$132.60
Purchase #7	$243.69	4.173%	$253.8592	$253.86	$253.85	$253.90
7 purchase totals =	$1,210.37		$1,292.8214	$1,292.82	$1,292.75	$1,292.80