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	$226.94	10.516%	$250.805	$250.81	$250.80	$250.80
Purchase #2	$78.46	6.289%	$83.3943	$83.39	$83.40	$83.40
Purchase #3	$28.82	13.778%	$32.7908	$32.79	$32.80	$32.80
Purchase #4	$44.40	4.251%	$46.2874	$46.29	$46.30	$46.30
Purchase #5	$124.65	6.626%	$132.9093	$132.91	$132.90	$132.90
Purchase #6	$81.67	10.259%	$90.0485	$90.05	$90.05	$90.00
Purchase #7	$73.99	4.705%	$77.4712	$77.47	$77.45	$77.50
7 purchase totals =	$658.93		$713.7065	$713.71	$713.70	$713.70