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	$47.84	6.353%	$50.8793	$50.88	$50.90	$50.90
Purchase #2	$206.97	12.595%	$233.0379	$233.04	$233.05	$233.00
Purchase #3	$43.34	7.716%	$46.6841	$46.68	$46.70	$46.70
Purchase #4	$118.71	7.111%	$127.1515	$127.15	$127.15	$127.20
Purchase #5	$88.92	7.739%	$95.8015	$95.80	$95.80	$95.80
Purchase #6	$42.72	9.140%	$46.6246	$46.62	$46.60	$46.60
Purchase #7	$139.79	9.439%	$152.9848	$152.98	$153.00	$153.00
7 purchase totals =	$688.29		$753.1637	$753.15	$753.20	$753.20