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	$55.38	6.742%	$59.1137	$59.11	$59.10	$59.10
Purchase #2	$102.28	4.316%	$106.6944	$106.69	$106.70	$106.70
Purchase #3	$128.43	11.109%	$142.6973	$142.70	$142.70	$142.70
Purchase #4	$30.86	9.242%	$33.7121	$33.71	$33.70	$33.70
Purchase #5	$64.89	13.477%	$73.6352	$73.64	$73.65	$73.60
Purchase #6	$159.67	7.422%	$171.5207	$171.52	$171.50	$171.50
Purchase #7	$19.99	7.695%	$21.5282	$21.53	$21.55	$21.50
7 purchase totals =	$561.50		$608.9016	$608.90	$608.90	$608.80