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	$59.95	11.469%	$66.8257	$66.83	$66.85	$66.80
Purchase #2	$130.29	4.428%	$136.0592	$136.06	$136.05	$136.10
Purchase #3	$30.95	3.115%	$31.9141	$31.91	$31.90	$31.90
Purchase #4	$169.56	4.112%	$176.5323	$176.53	$176.55	$176.50
Purchase #5	$173.97	4.160%	$181.2072	$181.21	$181.20	$181.20
Purchase #6	$71.71	9.810%	$78.7448	$78.74	$78.75	$78.70
Purchase #7	$12.72	6.634%	$13.5638	$13.56	$13.55	$13.60
7 purchase totals =	$649.15		$684.8471	$684.84	$684.85	$684.80