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	$10.61	7.297%	$11.3842	$11.38	$11.40	$11.40
Purchase #2	$82.28	3.711%	$85.3334	$85.33	$85.35	$85.30
Purchase #3	$236.29	9.474%	$258.6761	$258.68	$258.70	$258.70
Purchase #4	$138.36	9.720%	$151.8086	$151.81	$151.80	$151.80
Purchase #5	$245.77	9.804%	$269.8653	$269.87	$269.85	$269.90
Purchase #6	$39.90	13.450%	$45.2666	$45.27	$45.25	$45.30
Purchase #7	$90.72	3.802%	$94.1692	$94.17	$94.15	$94.20
7 purchase totals =	$843.93		$916.5034	$916.51	$916.50	$916.60