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	$86.69	4.391%	$90.4966	$90.50	$90.50	$90.50
Purchase #2	$235.83	10.766%	$261.2195	$261.22	$261.20	$261.20
Purchase #3	$58.68	12.267%	$65.8783	$65.88	$65.90	$65.90
Purchase #4	$62.41	8.566%	$67.756	$67.76	$67.75	$67.80
Purchase #5	$12.92	11.265%	$14.3754	$14.38	$14.40	$14.40
Purchase #6	$45.28	8.380%	$49.0745	$49.07	$49.05	$49.10
Purchase #7	$35.83	3.793%	$37.189	$37.19	$37.20	$37.20
7 purchase totals =	$537.64		$585.9893	$586.00	$586.00	$586.10