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	$171.53	10.411%	$189.388	$189.39	$189.40	$189.40
Purchase #2	$49.50	9.448%	$54.1768	$54.18	$54.20	$54.20
Purchase #3	$61.78	9.349%	$67.5558	$67.56	$67.55	$67.60
Purchase #4	$244.48	10.621%	$270.4462	$270.45	$270.45	$270.40
Purchase #5	$17.74	10.373%	$19.5802	$19.58	$19.60	$19.60
Purchase #6	$12.46	5.547%	$13.1512	$13.15	$13.15	$13.20
Purchase #7	$148.59	11.783%	$166.0984	$166.10	$166.10	$166.10
7 purchase totals =	$706.08		$780.3966	$780.41	$780.45	$780.50