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	$41.57	9.520%	$45.5275	$45.53	$45.55	$45.50
Purchase #2	$103.69	12.638%	$116.7943	$116.79	$116.80	$116.80
Purchase #3	$12.31	13.135%	$13.9269	$13.93	$13.95	$13.90
Purchase #4	$76.73	6.165%	$81.4604	$81.46	$81.45	$81.50
Purchase #5	$93.85	5.757%	$99.2529	$99.25	$99.25	$99.30
Purchase #6	$67.77	4.766%	$70.9999	$71.00	$71.00	$71.00
Purchase #7	$149.28	12.608%	$168.1012	$168.10	$168.10	$168.10
7 purchase totals =	$545.20		$596.0631	$596.06	$596.10	$596.10