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	$172.49	8.700%	$187.4966	$187.50	$187.50	$187.50
Purchase #2	$57.28	9.652%	$62.8087	$62.81	$62.80	$62.80
Purchase #3	$223.93	13.603%	$254.3912	$254.39	$254.40	$254.40
Purchase #4	$39.54	9.389%	$43.2524	$43.25	$43.25	$43.30
Purchase #5	$193.81	8.585%	$210.4486	$210.45	$210.45	$210.40
Purchase #6	$154.86	3.438%	$160.1841	$160.18	$160.20	$160.20
Purchase #7	$172.40	10.675%	$190.8037	$190.80	$190.80	$190.80
7 purchase totals =	$1,014.31		$1,109.3853	$1,109.38	$1,109.40	$1,109.40