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	$83.91	7.526%	$90.2251	$90.23	$90.25	$90.20
Purchase #2	$62.69	4.631%	$65.5932	$65.59	$65.60	$65.60
Purchase #3	$149.49	5.399%	$157.561	$157.56	$157.55	$157.60
Purchase #4	$79.71	12.163%	$89.4051	$89.41	$89.40	$89.40
Purchase #5	$238.38	11.532%	$265.87	$265.87	$265.85	$265.90
Purchase #6	$198.96	8.179%	$215.2329	$215.23	$215.25	$215.20
Purchase #7	$97.46	11.323%	$108.4954	$108.50	$108.50	$108.50
7 purchase totals =	$910.60		$992.3827	$992.39	$992.40	$992.40