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	$213.51	13.129%	$241.5417	$241.54	$241.55	$241.50
Purchase #2	$93.50	6.768%	$99.8281	$99.83	$99.85	$99.80
Purchase #3	$107.33	11.857%	$120.0561	$120.06	$120.05	$120.10
Purchase #4	$141.51	5.617%	$149.4586	$149.46	$149.45	$149.50
Purchase #5	$39.29	10.546%	$43.4335	$43.43	$43.45	$43.40
Purchase #6	$122.65	8.609%	$133.2089	$133.21	$133.20	$133.20
Purchase #7	$98.49	13.543%	$111.8285	$111.83	$111.85	$111.80
7 purchase totals =	$816.28		$899.3554	$899.36	$899.40	$899.30