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	$249.48	6.178%	$264.8929	$264.89	$264.90	$264.90
Purchase #2	$149.98	5.580%	$158.3489	$158.35	$158.35	$158.30
Purchase #3	$97.98	5.460%	$103.3297	$103.33	$103.35	$103.30
Purchase #4	$179.54	13.308%	$203.4332	$203.43	$203.45	$203.40
Purchase #5	$97.48	3.498%	$100.8899	$100.89	$100.90	$100.90
Purchase #6	$66.47	6.615%	$70.867	$70.87	$70.85	$70.90
Purchase #7	$103.90	13.852%	$118.2922	$118.29	$118.30	$118.30
7 purchase totals =	$944.83		$1,020.0538	$1,020.05	$1,020.10	$1,020.00