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	$106.92	10.158%	$117.7809	$117.78	$117.80	$117.80
Purchase #2	$65.68	3.300%	$67.8474	$67.85	$67.85	$67.80
Purchase #3	$171.28	4.444%	$178.8917	$178.89	$178.90	$178.90
Purchase #4	$45.48	4.664%	$47.6012	$47.60	$47.60	$47.60
Purchase #5	$62.83	11.601%	$70.1189	$70.12	$70.10	$70.10
Purchase #6	$130.71	12.322%	$146.8161	$146.82	$146.80	$146.80
Purchase #7	$192.64	11.814%	$215.3985	$215.40	$215.40	$215.40
7 purchase totals =	$775.54		$844.4547	$844.46	$844.45	$844.40