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	$71.48	13.396%	$81.0555	$81.06	$81.05	$81.10
Purchase #2	$175.85	13.871%	$200.2422	$200.24	$200.25	$200.20
Purchase #3	$24.95	6.130%	$26.4794	$26.48	$26.50	$26.50
Purchase #4	$128.62	9.843%	$141.2801	$141.28	$141.30	$141.30
Purchase #5	$158.27	6.470%	$168.5101	$168.51	$168.50	$168.50
Purchase #6	$97.48	6.773%	$104.0823	$104.08	$104.10	$104.10
Purchase #7	$53.76	9.428%	$58.8285	$58.83	$58.85	$58.80
7 purchase totals =	$710.41		$780.4781	$780.48	$780.55	$780.50