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	$80.80	3.617%	$83.7225	$83.72	$83.70	$83.70
Purchase #2	$183.85	11.755%	$205.4616	$205.46	$205.45	$205.50
Purchase #3	$215.97	8.400%	$234.1115	$234.11	$234.10	$234.10
Purchase #4	$191.75	12.720%	$216.1406	$216.14	$216.15	$216.10
Purchase #5	$127.45	11.453%	$142.0468	$142.05	$142.05	$142.00
Purchase #6	$162.67	6.178%	$172.7198	$172.72	$172.70	$172.70
Purchase #7	$120.79	5.857%	$127.8647	$127.86	$127.85	$127.90
7 purchase totals =	$1,083.28		$1,182.0675	$1,182.06	$1,182.00	$1,182.00