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	$209.34	5.685%	$221.241	$221.24	$221.25	$221.20
Purchase #2	$41.87	5.386%	$44.1251	$44.13	$44.15	$44.10
Purchase #3	$144.36	6.177%	$153.2771	$153.28	$153.30	$153.30
Purchase #4	$144.32	4.232%	$150.4276	$150.43	$150.45	$150.40
Purchase #5	$42.54	4.460%	$44.4373	$44.44	$44.45	$44.40
Purchase #6	$83.42	7.558%	$89.7249	$89.72	$89.70	$89.70
Purchase #7	$106.28	6.586%	$113.2796	$113.28	$113.30	$113.30
7 purchase totals =	$772.13		$816.5126	$816.52	$816.60	$816.40