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	$46.63	8.472%	$50.5805	$50.58	$50.60	$50.60
Purchase #2	$48.60	6.309%	$51.6662	$51.67	$51.65	$51.70
Purchase #3	$98.70	11.332%	$109.8847	$109.88	$109.90	$109.90
Purchase #4	$57.88	13.447%	$65.6631	$65.66	$65.65	$65.70
Purchase #5	$240.26	11.584%	$268.0917	$268.09	$268.10	$268.10
Purchase #6	$46.47	4.322%	$48.4784	$48.48	$48.50	$48.50
Purchase #7	$81.71	9.376%	$89.3711	$89.37	$89.35	$89.40
7 purchase totals =	$620.25		$683.7357	$683.73	$683.75	$683.90