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	$229.88	4.589%	$240.4292	$240.43	$240.45	$240.40
Purchase #2	$49.27	11.319%	$54.8469	$54.85	$54.85	$54.80
Purchase #3	$77.42	10.851%	$85.8208	$85.82	$85.80	$85.80
Purchase #4	$94.92	9.390%	$103.833	$103.83	$103.85	$103.80
Purchase #5	$237.33	6.804%	$253.4779	$253.48	$253.50	$253.50
Purchase #6	$164.87	6.614%	$175.7745	$175.77	$175.75	$175.80
Purchase #7	$45.35	6.137%	$48.1331	$48.13	$48.15	$48.10
7 purchase totals =	$899.04		$962.3154	$962.31	$962.35	$962.20