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	$114.48	12.297%	$128.5576	$128.56	$128.55	$128.60
Purchase #2	$151.88	11.109%	$168.7523	$168.75	$168.75	$168.80
Purchase #3	$224.64	10.725%	$248.7326	$248.73	$248.75	$248.70
Purchase #4	$120.88	5.104%	$127.0497	$127.05	$127.05	$127.00
Purchase #5	$48.93	3.231%	$50.5109	$50.51	$50.50	$50.50
Purchase #6	$146.89	10.834%	$162.8041	$162.80	$162.80	$162.80
Purchase #7	$183.38	11.790%	$205.0005	$205.00	$205.00	$205.00
7 purchase totals =	$991.08		$1,091.4077	$1,091.40	$1,091.40	$1,091.40