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	$148.87	3.329%	$153.8259	$153.83	$153.85	$153.80
Purchase #2	$136.65	4.679%	$143.0439	$143.04	$143.05	$143.00
Purchase #3	$42.32	10.703%	$46.8495	$46.85	$46.85	$46.80
Purchase #4	$18.58	9.817%	$20.404	$20.40	$20.40	$20.40
Purchase #5	$62.46	3.775%	$64.8179	$64.82	$64.80	$64.80
Purchase #6	$48.88	10.251%	$53.8907	$53.89	$53.90	$53.90
Purchase #7	$59.32	12.753%	$66.8851	$66.89	$66.90	$66.90
7 purchase totals =	$517.08		$549.7170	$549.72	$549.75	$549.60