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	$37.32	13.242%	$42.2619	$42.26	$42.25	$42.30
Purchase #2	$213.45	4.679%	$223.4373	$223.44	$223.45	$223.40
Purchase #3	$172.31	10.683%	$190.7179	$190.72	$190.70	$190.70
Purchase #4	$189.74	13.443%	$215.2467	$215.25	$215.25	$215.20
Purchase #5	$247.48	10.465%	$273.3788	$273.38	$273.40	$273.40
Purchase #6	$148.58	9.160%	$162.1899	$162.19	$162.20	$162.20
Purchase #7	$11.44	9.268%	$12.5003	$12.50	$12.50	$12.50
7 purchase totals =	$1,020.32		$1,119.7328	$1,119.74	$1,119.75	$1,119.70