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	$233.53	9.356%	$255.3791	$255.38	$255.40	$255.40
Purchase #2	$227.76	13.118%	$257.6376	$257.64	$257.65	$257.60
Purchase #3	$175.98	8.163%	$190.3452	$190.35	$190.35	$190.30
Purchase #4	$98.71	13.272%	$111.8108	$111.81	$111.80	$111.80
Purchase #5	$67.65	4.528%	$70.7132	$70.71	$70.70	$70.70
Purchase #6	$5.64	7.303%	$6.0519	$6.05	$6.05	$6.10
Purchase #7	$80.28	12.404%	$90.2379	$90.24	$90.25	$90.20
7 purchase totals =	$889.55		$982.1757	$982.18	$982.20	$982.10