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	$206.74	10.743%	$228.9501	$228.95	$228.95	$229.00
Purchase #2	$19.26	6.617%	$20.5344	$20.53	$20.55	$20.50
Purchase #3	$200.79	13.313%	$227.5212	$227.52	$227.50	$227.50
Purchase #4	$110.63	7.149%	$118.5389	$118.54	$118.55	$118.50
Purchase #5	$149.91	8.466%	$162.6014	$162.60	$162.60	$162.60
Purchase #6	$31.95	4.188%	$33.2881	$33.29	$33.30	$33.30
Purchase #7	$63.51	6.122%	$67.3981	$67.40	$67.40	$67.40
7 purchase totals =	$782.79		$858.8322	$858.83	$858.85	$858.80