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	$170.40	5.119%	$179.1228	$179.12	$179.10	$179.10
Purchase #2	$155.87	9.283%	$170.3394	$170.34	$170.35	$170.30
Purchase #3	$152.38	6.683%	$162.5636	$162.56	$162.55	$162.60
Purchase #4	$95.64	13.532%	$108.582	$108.58	$108.60	$108.60
Purchase #5	$67.45	11.765%	$75.3855	$75.39	$75.40	$75.40
Purchase #6	$52.75	13.204%	$59.7151	$59.72	$59.70	$59.70
Purchase #7	$36.96	10.760%	$40.9369	$40.94	$40.95	$40.90
7 purchase totals =	$731.45		$796.6453	$796.65	$796.65	$796.60