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	$44.32	6.777%	$47.3236	$47.32	$47.30	$47.30
Purchase #2	$77.49	7.239%	$83.0995	$83.10	$83.10	$83.10
Purchase #3	$90.67	13.476%	$102.8887	$102.89	$102.90	$102.90
Purchase #4	$128.59	11.596%	$143.5013	$143.50	$143.50	$143.50
Purchase #5	$185.32	10.165%	$204.1578	$204.16	$204.15	$204.20
Purchase #6	$31.72	6.379%	$33.7434	$33.74	$33.75	$33.70
Purchase #7	$167.99	12.873%	$189.6154	$189.62	$189.60	$189.60
7 purchase totals =	$726.10		$804.3297	$804.33	$804.30	$804.30