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	$42.70	9.347%	$46.6912	$46.69	$46.70	$46.70
Purchase #2	$60.56	7.666%	$65.2025	$65.20	$65.20	$65.20
Purchase #3	$123.77	10.151%	$136.3339	$136.33	$136.35	$136.30
Purchase #4	$127.49	9.624%	$139.7596	$139.76	$139.75	$139.80
Purchase #5	$37.99	9.598%	$41.6363	$41.64	$41.65	$41.60
Purchase #6	$164.71	4.685%	$172.4267	$172.43	$172.45	$172.40
Purchase #7	$151.83	3.284%	$156.8161	$156.82	$156.80	$156.80
7 purchase totals =	$709.05		$758.8663	$758.87	$758.90	$758.80