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	$159.50	12.383%	$179.2509	$179.25	$179.25	$179.30
Purchase #2	$148.58	11.705%	$165.9713	$165.97	$165.95	$166.00
Purchase #3	$242.58	5.769%	$256.5744	$256.57	$256.55	$256.60
Purchase #4	$91.53	13.488%	$103.8756	$103.88	$103.90	$103.90
Purchase #5	$215.57	12.646%	$242.831	$242.83	$242.85	$242.80
Purchase #6	$140.84	8.835%	$153.2832	$153.28	$153.30	$153.30
Purchase #7	$47.29	4.558%	$49.4455	$49.45	$49.45	$49.40
7 purchase totals =	$1,045.89		$1,151.2319	$1,151.23	$1,151.25	$1,151.30