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	$181.89	4.394%	$189.8822	$189.88	$189.90	$189.90
Purchase #2	$156.63	8.399%	$169.7854	$169.79	$169.80	$169.80
Purchase #3	$247.46	11.237%	$275.2671	$275.27	$275.25	$275.30
Purchase #4	$185.72	10.123%	$204.5204	$204.52	$204.50	$204.50
Purchase #5	$86.97	3.300%	$89.84	$89.84	$89.85	$89.80
Purchase #6	$198.68	4.501%	$207.6226	$207.62	$207.60	$207.60
Purchase #7	$133.76	6.363%	$142.2711	$142.27	$142.25	$142.30
7 purchase totals =	$1,191.11		$1,279.1888	$1,279.19	$1,279.15	$1,279.20