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	$60.85	11.416%	$67.7966	$67.80	$67.80	$67.80
Purchase #2	$104.42	10.193%	$115.0635	$115.06	$115.05	$115.10
Purchase #3	$57.91	3.782%	$60.1002	$60.10	$60.10	$60.10
Purchase #4	$87.36	3.181%	$90.1389	$90.14	$90.15	$90.10
Purchase #5	$157.51	13.715%	$179.1125	$179.11	$179.10	$179.10
Purchase #6	$176.92	6.445%	$188.3225	$188.32	$188.30	$188.30
Purchase #7	$93.74	5.764%	$99.1432	$99.14	$99.15	$99.10
7 purchase totals =	$738.71		$799.6774	$799.67	$799.65	$799.60