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	$112.93	8.164%	$122.1496	$122.15	$122.15	$122.10
Purchase #2	$105.56	4.761%	$110.5857	$110.59	$110.60	$110.60
Purchase #3	$237.83	6.150%	$252.4565	$252.46	$252.45	$252.50
Purchase #4	$82.31	4.188%	$85.7571	$85.76	$85.75	$85.80
Purchase #5	$82.36	10.781%	$91.2392	$91.24	$91.25	$91.20
Purchase #6	$128.63	10.222%	$141.7786	$141.78	$141.80	$141.80
Purchase #7	$58.78	4.841%	$61.6255	$61.63	$61.65	$61.60
7 purchase totals =	$808.40		$865.5922	$865.61	$865.65	$865.60