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	$28.30	5.542%	$29.8684	$29.87	$29.85	$29.90
Purchase #2	$65.61	12.663%	$73.9182	$73.92	$73.90	$73.90
Purchase #3	$35.61	11.151%	$39.5809	$39.58	$39.60	$39.60
Purchase #4	$52.33	5.396%	$55.1537	$55.15	$55.15	$55.20
Purchase #5	$207.82	3.692%	$215.4927	$215.49	$215.50	$215.50
Purchase #6	$160.91	6.593%	$171.5188	$171.52	$171.50	$171.50
Purchase #7	$36.47	3.722%	$37.8274	$37.83	$37.85	$37.80
7 purchase totals =	$587.05		$623.3601	$623.36	$623.35	$623.40