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	$162.46	12.689%	$183.0745	$183.07	$183.05	$183.10
Purchase #2	$235.38	12.544%	$264.9061	$264.91	$264.90	$264.90
Purchase #3	$199.30	8.495%	$216.2305	$216.23	$216.25	$216.20
Purchase #4	$74.66	12.123%	$83.711	$83.71	$83.70	$83.70
Purchase #5	$196.65	12.548%	$221.3256	$221.33	$221.35	$221.30
Purchase #6	$86.71	4.636%	$90.7299	$90.73	$90.75	$90.70
Purchase #7	$126.63	9.406%	$138.5408	$138.54	$138.55	$138.50
7 purchase totals =	$1,081.79		$1,198.5184	$1,198.52	$1,198.55	$1,198.40