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	$19.51	10.525%	$21.5634	$21.56	$21.55	$21.60
Purchase #2	$128.52	12.174%	$144.166	$144.17	$144.15	$144.20
Purchase #3	$207.39	12.678%	$233.6829	$233.68	$233.70	$233.70
Purchase #4	$31.36	12.370%	$35.2392	$35.24	$35.25	$35.20
Purchase #5	$102.32	3.263%	$105.6587	$105.66	$105.65	$105.70
Purchase #6	$53.36	6.558%	$56.8593	$56.86	$56.85	$56.90
Purchase #7	$54.66	13.151%	$61.8483	$61.85	$61.85	$61.80
7 purchase totals =	$597.12		$659.0178	$659.02	$659.00	$659.10