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	$209.66	13.590%	$238.1528	$238.15	$238.15	$238.20
Purchase #2	$221.70	11.697%	$247.6322	$247.63	$247.65	$247.60
Purchase #3	$37.56	4.338%	$39.1894	$39.19	$39.20	$39.20
Purchase #4	$108.96	8.768%	$118.5136	$118.51	$118.50	$118.50
Purchase #5	$148.91	9.417%	$162.9329	$162.93	$162.95	$162.90
Purchase #6	$37.39	3.485%	$38.693	$38.69	$38.70	$38.70
Purchase #7	$81.86	5.560%	$86.4114	$86.41	$86.40	$86.40
7 purchase totals =	$846.04		$931.5253	$931.51	$931.55	$931.50