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	$235.83	6.123%	$250.2699	$250.27	$250.25	$250.30
Purchase #2	$100.74	5.111%	$105.8888	$105.89	$105.90	$105.90
Purchase #3	$94.71	5.433%	$99.8556	$99.86	$99.85	$99.90
Purchase #4	$89.40	13.683%	$101.6326	$101.63	$101.65	$101.60
Purchase #5	$17.34	11.376%	$19.3126	$19.31	$19.30	$19.30
Purchase #6	$158.95	8.473%	$172.4178	$172.42	$172.40	$172.40
Purchase #7	$234.71	11.705%	$262.1828	$262.18	$262.20	$262.20
7 purchase totals =	$931.68		$1,011.5601	$1,011.56	$1,011.55	$1,011.60