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	$104.54	12.822%	$117.9441	$117.94	$117.95	$117.90
Purchase #2	$49.89	7.675%	$53.7191	$53.72	$53.70	$53.70
Purchase #3	$188.54	6.705%	$201.1816	$201.18	$201.20	$201.20
Purchase #4	$193.93	11.293%	$215.8305	$215.83	$215.85	$215.80
Purchase #5	$18.32	6.549%	$19.5198	$19.52	$19.50	$19.50
Purchase #6	$122.77	13.551%	$139.4066	$139.41	$139.40	$139.40
Purchase #7	$238.80	6.848%	$255.153	$255.15	$255.15	$255.20
7 purchase totals =	$916.79		$1,002.7547	$1,002.75	$1,002.75	$1,002.70