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	$20.82	4.867%	$21.8333	$21.83	$21.85	$21.80
Purchase #2	$128.41	8.842%	$139.764	$139.76	$139.75	$139.80
Purchase #3	$94.54	13.288%	$107.1025	$107.10	$107.10	$107.10
Purchase #4	$165.36	10.685%	$183.0287	$183.03	$183.05	$183.00
Purchase #5	$43.35	7.467%	$46.5869	$46.59	$46.60	$46.60
Purchase #6	$40.95	3.640%	$42.4406	$42.44	$42.45	$42.40
Purchase #7	$163.33	5.371%	$172.1025	$172.10	$172.10	$172.10
7 purchase totals =	$656.76		$712.8585	$712.85	$712.90	$712.80