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	$98.78	6.383%	$105.0851	$105.09	$105.10	$105.10
Purchase #2	$83.96	7.629%	$90.3653	$90.37	$90.35	$90.40
Purchase #3	$46.81	10.604%	$51.7737	$51.77	$51.75	$51.80
Purchase #4	$101.64	12.285%	$114.1265	$114.13	$114.15	$114.10
Purchase #5	$140.88	8.346%	$152.6378	$152.64	$152.65	$152.60
Purchase #6	$46.43	6.265%	$49.3388	$49.34	$49.35	$49.30
Purchase #7	$228.86	6.583%	$243.9259	$243.93	$243.95	$243.90
7 purchase totals =	$747.36		$807.2531	$807.27	$807.30	$807.20