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	$228.28	4.453%	$238.4453	$238.45	$238.45	$238.40
Purchase #2	$189.89	5.408%	$200.1593	$200.16	$200.15	$200.20
Purchase #3	$234.71	6.440%	$249.8253	$249.83	$249.85	$249.80
Purchase #4	$159.64	5.808%	$168.9119	$168.91	$168.90	$168.90
Purchase #5	$201.46	3.586%	$208.6844	$208.68	$208.70	$208.70
Purchase #6	$74.30	7.688%	$80.0122	$80.01	$80.00	$80.00
Purchase #7	$59.36	10.399%	$65.5328	$65.53	$65.55	$65.50
7 purchase totals =	$1,147.64		$1,211.5712	$1,211.57	$1,211.60	$1,211.50