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	$106.59	5.438%	$112.3864	$112.39	$112.40	$112.40
Purchase #2	$241.41	13.106%	$273.0492	$273.05	$273.05	$273.00
Purchase #3	$178.55	11.866%	$199.7367	$199.74	$199.75	$199.70
Purchase #4	$119.46	6.419%	$127.1281	$127.13	$127.15	$127.10
Purchase #5	$143.69	5.411%	$151.4651	$151.47	$151.45	$151.50
Purchase #6	$142.30	4.289%	$148.4032	$148.40	$148.40	$148.40
Purchase #7	$26.39	3.125%	$27.2147	$27.21	$27.20	$27.20
7 purchase totals =	$958.39		$1,039.3834	$1,039.39	$1,039.40	$1,039.30