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	$221.84	11.827%	$248.077	$248.08	$248.10	$248.10
Purchase #2	$47.94	6.793%	$51.1966	$51.20	$51.20	$51.20
Purchase #3	$83.98	8.339%	$90.9831	$90.98	$91.00	$91.00
Purchase #4	$30.51	7.156%	$32.6933	$32.69	$32.70	$32.70
Purchase #5	$215.84	11.442%	$240.5364	$240.54	$240.55	$240.50
Purchase #6	$52.95	11.746%	$59.1695	$59.17	$59.15	$59.20
Purchase #7	$165.29	12.185%	$185.4306	$185.43	$185.45	$185.40
7 purchase totals =	$818.35		$908.0865	$908.09	$908.15	$908.10