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	$7.84	10.194%	$8.6392	$8.64	$8.65	$8.60
Purchase #2	$188.64	5.754%	$199.4943	$199.49	$199.50	$199.50
Purchase #3	$224.97	8.240%	$243.5075	$243.51	$243.50	$243.50
Purchase #4	$53.96	6.654%	$57.5505	$57.55	$57.55	$57.60
Purchase #5	$124.92	7.511%	$134.3027	$134.30	$134.30	$134.30
Purchase #6	$81.47	11.388%	$90.7478	$90.75	$90.75	$90.70
Purchase #7	$158.59	4.559%	$165.8201	$165.82	$165.80	$165.80
7 purchase totals =	$840.39		$900.0621	$900.06	$900.05	$900.00