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	$48.80	6.262%	$51.8559	$51.86	$51.85	$51.90
Purchase #2	$178.53	4.450%	$186.4746	$186.47	$186.45	$186.50
Purchase #3	$174.67	12.308%	$196.1684	$196.17	$196.15	$196.20
Purchase #4	$126.73	5.656%	$133.8978	$133.90	$133.90	$133.90
Purchase #5	$203.99	9.476%	$223.3201	$223.32	$223.30	$223.30
Purchase #6	$233.77	9.103%	$255.0501	$255.05	$255.05	$255.10
Purchase #7	$191.75	10.704%	$212.2749	$212.27	$212.25	$212.30
7 purchase totals =	$1,158.24		$1,259.0418	$1,259.04	$1,258.95	$1,259.20