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	$67.49	7.418%	$72.4964	$72.50	$72.50	$72.50
Purchase #2	$228.98	3.405%	$236.7768	$236.78	$236.80	$236.80
Purchase #3	$19.32	11.748%	$21.5897	$21.59	$21.60	$21.60
Purchase #4	$59.30	13.642%	$67.3897	$67.39	$67.40	$67.40
Purchase #5	$222.61	9.180%	$243.0456	$243.05	$243.05	$243.00
Purchase #6	$70.30	13.787%	$79.9923	$79.99	$80.00	$80.00
Purchase #7	$151.25	4.544%	$158.1228	$158.12	$158.10	$158.10
7 purchase totals =	$819.25		$879.4133	$879.42	$879.45	$879.40