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	$243.57	11.837%	$272.4014	$272.40	$272.40	$272.40
Purchase #2	$40.87	7.134%	$43.7857	$43.79	$43.80	$43.80
Purchase #3	$58.71	9.325%	$64.1847	$64.18	$64.20	$64.20
Purchase #4	$199.40	4.708%	$208.7878	$208.79	$208.80	$208.80
Purchase #5	$73.84	11.496%	$82.3286	$82.33	$82.35	$82.30
Purchase #6	$105.34	10.563%	$116.4671	$116.47	$116.45	$116.50
Purchase #7	$118.31	6.729%	$126.2711	$126.27	$126.25	$126.30
7 purchase totals =	$840.04		$914.2264	$914.23	$914.25	$914.30