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	$158.49	12.580%	$178.428	$178.43	$178.45	$178.40
Purchase #2	$145.48	4.679%	$152.287	$152.29	$152.30	$152.30
Purchase #3	$74.27	6.268%	$78.9252	$78.93	$78.95	$78.90
Purchase #4	$96.97	5.792%	$102.5865	$102.59	$102.60	$102.60
Purchase #5	$118.91	13.283%	$134.7048	$134.70	$134.70	$134.70
Purchase #6	$80.26	12.679%	$90.4362	$90.44	$90.45	$90.40
Purchase #7	$132.57	6.821%	$141.6126	$141.61	$141.60	$141.60
7 purchase totals =	$806.95		$878.9803	$878.99	$879.05	$878.90