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	$18.55	12.583%	$20.8841	$20.88	$20.90	$20.90
Purchase #2	$46.59	4.687%	$48.7737	$48.77	$48.75	$48.80
Purchase #3	$142.74	6.670%	$152.2608	$152.26	$152.25	$152.30
Purchase #4	$16.91	10.287%	$18.6495	$18.65	$18.65	$18.60
Purchase #5	$178.45	10.192%	$196.6376	$196.64	$196.65	$196.60
Purchase #6	$49.53	3.490%	$51.2586	$51.26	$51.25	$51.30
Purchase #7	$70.33	12.707%	$79.2668	$79.27	$79.25	$79.30
7 purchase totals =	$523.10		$567.7311	$567.73	$567.70	$567.80