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	$79.73	13.772%	$90.7104	$90.71	$90.70	$90.70
Purchase #2	$120.73	11.421%	$134.5186	$134.52	$134.50	$134.50
Purchase #3	$57.34	4.672%	$60.0189	$60.02	$60.00	$60.00
Purchase #4	$13.98	6.470%	$14.8845	$14.88	$14.90	$14.90
Purchase #5	$204.79	6.123%	$217.3293	$217.33	$217.35	$217.30
Purchase #6	$59.62	12.168%	$66.8746	$66.87	$66.85	$66.90
Purchase #7	$106.31	6.713%	$113.4466	$113.45	$113.45	$113.40
7 purchase totals =	$642.50		$697.7829	$697.78	$697.75	$697.70