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	$127.47	6.343%	$135.5554	$135.56	$135.55	$135.60
Purchase #2	$125.44	5.117%	$131.8588	$131.86	$131.85	$131.90
Purchase #3	$103.60	4.676%	$108.4443	$108.44	$108.45	$108.40
Purchase #4	$40.55	12.838%	$45.7558	$45.76	$45.75	$45.80
Purchase #5	$203.73	12.693%	$229.5894	$229.59	$229.60	$229.60
Purchase #6	$240.91	11.825%	$269.3976	$269.40	$269.40	$269.40
Purchase #7	$57.25	3.727%	$59.3837	$59.38	$59.40	$59.40
7 purchase totals =	$898.95		$979.9850	$979.99	$980.00	$980.10