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	$115.71	5.865%	$122.4964	$122.50	$122.50	$122.50
Purchase #2	$242.68	6.874%	$259.3618	$259.36	$259.35	$259.40
Purchase #3	$157.53	11.380%	$175.4569	$175.46	$175.45	$175.50
Purchase #4	$78.93	4.251%	$82.2853	$82.29	$82.30	$82.30
Purchase #5	$72.89	13.350%	$82.6208	$82.62	$82.60	$82.60
Purchase #6	$148.65	13.217%	$168.2971	$168.30	$168.30	$168.30
Purchase #7	$123.88	3.184%	$127.8243	$127.82	$127.80	$127.80
7 purchase totals =	$940.27		$1,018.3426	$1,018.35	$1,018.30	$1,018.40