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	$243.76	10.691%	$269.8204	$269.82	$269.80	$269.80
Purchase #2	$90.39	10.181%	$99.5926	$99.59	$99.60	$99.60
Purchase #3	$102.93	3.762%	$106.8022	$106.80	$106.80	$106.80
Purchase #4	$177.73	10.313%	$196.0593	$196.06	$196.05	$196.10
Purchase #5	$165.27	6.735%	$176.4009	$176.40	$176.40	$176.40
Purchase #6	$162.46	10.150%	$178.9497	$178.95	$178.95	$178.90
Purchase #7	$168.65	9.188%	$184.1456	$184.15	$184.15	$184.10
7 purchase totals =	$1,111.19		$1,211.7707	$1,211.77	$1,211.75	$1,211.70