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	$148.82	7.256%	$159.6184	$159.62	$159.60	$159.60
Purchase #2	$110.82	11.564%	$123.6352	$123.64	$123.65	$123.60
Purchase #3	$222.71	8.429%	$241.4822	$241.48	$241.50	$241.50
Purchase #4	$245.36	11.129%	$272.6661	$272.67	$272.65	$272.70
Purchase #5	$57.43	9.510%	$62.8916	$62.89	$62.90	$62.90
Purchase #6	$99.94	9.104%	$109.0385	$109.04	$109.05	$109.00
Purchase #7	$185.53	4.323%	$193.5505	$193.55	$193.55	$193.60
7 purchase totals =	$1,070.61		$1,162.8825	$1,162.89	$1,162.90	$1,162.90