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	$208.98	5.779%	$221.057	$221.06	$221.05	$221.10
Purchase #2	$59.40	4.703%	$62.1936	$62.19	$62.20	$62.20
Purchase #3	$95.79	8.244%	$103.6869	$103.69	$103.70	$103.70
Purchase #4	$80.77	12.316%	$90.7176	$90.72	$90.70	$90.70
Purchase #5	$224.83	11.793%	$251.3442	$251.34	$251.35	$251.30
Purchase #6	$38.75	7.821%	$41.7806	$41.78	$41.80	$41.80
Purchase #7	$149.54	7.371%	$160.5626	$160.56	$160.55	$160.60
7 purchase totals =	$858.06		$931.3425	$931.34	$931.35	$931.40