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	$165.65	11.257%	$184.2972	$184.30	$184.30	$184.30
Purchase #2	$162.94	10.466%	$179.9933	$179.99	$180.00	$180.00
Purchase #3	$37.73	13.564%	$42.8477	$42.85	$42.85	$42.80
Purchase #4	$117.38	11.115%	$130.4268	$130.43	$130.45	$130.40
Purchase #5	$33.63	11.834%	$37.6098	$37.61	$37.60	$37.60
Purchase #6	$44.59	11.844%	$49.8712	$49.87	$49.85	$49.90
Purchase #7	$98.88	3.566%	$102.4061	$102.41	$102.40	$102.40
7 purchase totals =	$660.80		$727.4521	$727.46	$727.45	$727.40