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	$102.56	8.761%	$111.5453	$111.55	$111.55	$111.50
Purchase #2	$158.49	12.497%	$178.2965	$178.30	$178.30	$178.30
Purchase #3	$218.65	4.750%	$229.0359	$229.04	$229.05	$229.00
Purchase #4	$17.89	9.478%	$19.5856	$19.59	$19.60	$19.60
Purchase #5	$79.37	4.136%	$82.6527	$82.65	$82.65	$82.70
Purchase #6	$58.73	3.483%	$60.7756	$60.78	$60.80	$60.80
Purchase #7	$131.45	7.724%	$141.6032	$141.60	$141.60	$141.60
7 purchase totals =	$767.14		$823.4948	$823.51	$823.55	$823.50