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	$47.87	4.549%	$50.0476	$50.05	$50.05	$50.00
Purchase #2	$172.56	13.805%	$196.3819	$196.38	$196.40	$196.40
Purchase #3	$35.51	4.855%	$37.234	$37.23	$37.25	$37.20
Purchase #4	$130.49	8.425%	$141.4838	$141.48	$141.50	$141.50
Purchase #5	$108.57	6.170%	$115.2688	$115.27	$115.25	$115.30
Purchase #6	$101.61	10.194%	$111.9681	$111.97	$111.95	$112.00
Purchase #7	$63.45	10.642%	$70.2023	$70.20	$70.20	$70.20
7 purchase totals =	$660.06		$722.5865	$722.58	$722.60	$722.60