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	$10.60	11.506%	$11.8196	$11.82	$11.80	$11.80
Purchase #2	$87.48	10.796%	$96.9243	$96.92	$96.90	$96.90
Purchase #3	$214.86	7.817%	$231.6556	$231.66	$231.65	$231.70
Purchase #4	$248.67	7.765%	$267.9792	$267.98	$268.00	$268.00
Purchase #5	$238.45	8.525%	$258.7779	$258.78	$258.80	$258.80
Purchase #6	$59.94	12.639%	$67.5158	$67.52	$67.50	$67.50
Purchase #7	$30.69	10.248%	$33.8351	$33.84	$33.85	$33.80
7 purchase totals =	$890.69		$968.5075	$968.52	$968.50	$968.50