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	$31.58	7.295%	$33.8838	$33.88	$33.90	$33.90
Purchase #2	$53.25	8.684%	$57.8742	$57.87	$57.85	$57.90
Purchase #3	$172.42	11.553%	$192.3397	$192.34	$192.35	$192.30
Purchase #4	$80.91	10.475%	$89.3853	$89.39	$89.40	$89.40
Purchase #5	$7.25	7.170%	$7.7698	$7.77	$7.75	$7.80
Purchase #6	$80.57	4.131%	$83.8983	$83.90	$83.90	$83.90
Purchase #7	$166.28	10.641%	$183.9739	$183.97	$183.95	$184.00
7 purchase totals =	$592.26		$649.1250	$649.12	$649.10	$649.20