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	$108.81	13.624%	$123.6343	$123.63	$123.65	$123.60
Purchase #2	$96.53	7.207%	$103.4869	$103.49	$103.50	$103.50
Purchase #3	$128.50	7.799%	$138.5217	$138.52	$138.50	$138.50
Purchase #4	$197.50	7.461%	$212.2355	$212.24	$212.25	$212.20
Purchase #5	$240.95	3.585%	$249.5881	$249.59	$249.60	$249.60
Purchase #6	$133.71	5.734%	$141.3769	$141.38	$141.40	$141.40
Purchase #7	$50.85	4.224%	$52.9979	$53.00	$53.00	$53.00
7 purchase totals =	$956.85		$1,021.8413	$1,021.85	$1,021.90	$1,021.80