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	$82.39	13.765%	$93.731	$93.73	$93.75	$93.70
Purchase #2	$137.30	4.722%	$143.7833	$143.78	$143.80	$143.80
Purchase #3	$249.40	5.553%	$263.2492	$263.25	$263.25	$263.20
Purchase #4	$216.49	6.635%	$230.8541	$230.85	$230.85	$230.90
Purchase #5	$90.38	10.740%	$100.0868	$100.09	$100.10	$100.10
Purchase #6	$248.37	13.327%	$281.4703	$281.47	$281.45	$281.50
Purchase #7	$225.97	3.315%	$233.4609	$233.46	$233.45	$233.50
7 purchase totals =	$1,250.30		$1,346.6356	$1,346.63	$1,346.65	$1,346.70