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	$13.78	5.621%	$14.5546	$14.55	$14.55	$14.60
Purchase #2	$116.77	9.379%	$127.7219	$127.72	$127.70	$127.70
Purchase #3	$124.62	4.743%	$130.5307	$130.53	$130.55	$130.50
Purchase #4	$38.77	8.436%	$42.0406	$42.04	$42.05	$42.00
Purchase #5	$126.29	4.479%	$131.9465	$131.95	$131.95	$131.90
Purchase #6	$180.26	6.254%	$191.5335	$191.53	$191.55	$191.50
Purchase #7	$151.36	7.198%	$162.2549	$162.25	$162.25	$162.30
7 purchase totals =	$751.85		$800.5827	$800.57	$800.60	$800.50