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	$238.93	4.539%	$249.775	$249.78	$249.80	$249.80
Purchase #2	$128.82	9.813%	$141.4611	$141.46	$141.45	$141.50
Purchase #3	$138.42	5.179%	$145.5888	$145.59	$145.60	$145.60
Purchase #4	$111.39	12.288%	$125.0776	$125.08	$125.10	$125.10
Purchase #5	$87.76	3.847%	$91.1361	$91.14	$91.15	$91.10
Purchase #6	$124.56	3.441%	$128.8461	$128.85	$128.85	$128.80
Purchase #7	$165.75	5.589%	$175.0138	$175.01	$175.00	$175.00
7 purchase totals =	$995.63		$1,056.8985	$1,056.91	$1,056.95	$1,056.90