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	$53.69	5.399%	$56.5887	$56.59	$56.60	$56.60
Purchase #2	$126.63	11.714%	$141.4634	$141.46	$141.45	$141.50
Purchase #3	$171.26	5.490%	$180.6622	$180.66	$180.65	$180.70
Purchase #4	$223.95	8.683%	$243.3956	$243.40	$243.40	$243.40
Purchase #5	$91.56	9.336%	$100.108	$100.11	$100.10	$100.10
Purchase #6	$99.41	5.315%	$104.6936	$104.69	$104.70	$104.70
Purchase #7	$172.64	3.305%	$178.3458	$178.35	$178.35	$178.30
7 purchase totals =	$939.14		$1,005.2573	$1,005.26	$1,005.25	$1,005.30