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	$228.55	8.463%	$247.8922	$247.89	$247.90	$247.90
Purchase #2	$148.60	4.816%	$155.7566	$155.76	$155.75	$155.80
Purchase #3	$195.69	8.418%	$212.1632	$212.16	$212.15	$212.20
Purchase #4	$117.74	5.119%	$123.7671	$123.77	$123.75	$123.80
Purchase #5	$177.96	5.110%	$187.0538	$187.05	$187.05	$187.10
Purchase #6	$101.44	6.790%	$108.3278	$108.33	$108.35	$108.30
Purchase #7	$117.59	5.335%	$123.8634	$123.86	$123.85	$123.90
7 purchase totals =	$1,087.57		$1,158.8241	$1,158.82	$1,158.80	$1,159.00