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	$137.92	11.362%	$153.5905	$153.59	$153.60	$153.60
Purchase #2	$165.57	4.182%	$172.4941	$172.49	$172.50	$172.50
Purchase #3	$38.36	12.137%	$43.0158	$43.02	$43.00	$43.00
Purchase #4	$136.43	4.608%	$142.7167	$142.72	$142.70	$142.70
Purchase #5	$180.84	7.454%	$194.3198	$194.32	$194.30	$194.30
Purchase #6	$16.87	4.234%	$17.5843	$17.58	$17.60	$17.60
Purchase #7	$103.97	7.297%	$111.5567	$111.56	$111.55	$111.60
7 purchase totals =	$779.96		$835.2779	$835.28	$835.25	$835.30