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	$100.30	3.127%	$103.4364	$103.44	$103.45	$103.40
Purchase #2	$84.75	6.762%	$90.4808	$90.48	$90.50	$90.50
Purchase #3	$134.80	3.354%	$139.3212	$139.32	$139.30	$139.30
Purchase #4	$101.46	6.666%	$108.2233	$108.22	$108.20	$108.20
Purchase #5	$12.26	11.366%	$13.6535	$13.65	$13.65	$13.70
Purchase #6	$225.76	10.726%	$249.975	$249.98	$250.00	$250.00
Purchase #7	$70.77	12.650%	$79.7224	$79.72	$79.70	$79.70
7 purchase totals =	$730.10		$784.8126	$784.81	$784.80	$784.80