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	$103.46	12.496%	$116.3884	$116.39	$116.40	$116.40
Purchase #2	$208.37	5.476%	$219.7803	$219.78	$219.80	$219.80
Purchase #3	$141.52	5.632%	$149.4904	$149.49	$149.50	$149.50
Purchase #4	$134.39	11.815%	$150.2682	$150.27	$150.25	$150.30
Purchase #5	$113.65	6.137%	$120.6247	$120.62	$120.60	$120.60
Purchase #6	$146.55	11.139%	$162.8742	$162.87	$162.85	$162.90
Purchase #7	$66.44	8.288%	$71.9465	$71.95	$71.95	$71.90
7 purchase totals =	$914.38		$991.3727	$991.37	$991.35	$991.40