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	$223.82	8.209%	$242.1934	$242.19	$242.20	$242.20
Purchase #2	$158.55	13.319%	$179.6673	$179.67	$179.65	$179.70
Purchase #3	$32.37	10.249%	$35.6876	$35.69	$35.70	$35.70
Purchase #4	$112.96	9.477%	$123.6652	$123.67	$123.65	$123.70
Purchase #5	$5.86	10.111%	$6.4525	$6.45	$6.45	$6.50
Purchase #6	$28.82	11.641%	$32.1749	$32.17	$32.15	$32.20
Purchase #7	$104.66	9.643%	$114.7524	$114.75	$114.75	$114.80
7 purchase totals =	$667.04		$734.5933	$734.59	$734.55	$734.80