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	$208.70	12.747%	$235.303	$235.30	$235.30	$235.30
Purchase #2	$176.62	12.277%	$198.3036	$198.30	$198.30	$198.30
Purchase #3	$184.93	8.222%	$200.1349	$200.13	$200.15	$200.10
Purchase #4	$6.54	4.347%	$6.8243	$6.82	$6.80	$6.80
Purchase #5	$54.87	13.614%	$62.34	$62.34	$62.35	$62.30
Purchase #6	$25.87	10.469%	$28.5783	$28.58	$28.60	$28.60
Purchase #7	$116.25	6.167%	$123.4191	$123.42	$123.40	$123.40
7 purchase totals =	$773.78		$854.9032	$854.89	$854.90	$854.80