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	$245.59	13.773%	$279.4151	$279.42	$279.40	$279.40
Purchase #2	$177.91	7.720%	$191.6447	$191.64	$191.65	$191.60
Purchase #3	$165.45	7.751%	$178.274	$178.27	$178.25	$178.30
Purchase #4	$149.40	13.794%	$170.0082	$170.01	$170.00	$170.00
Purchase #5	$62.34	7.735%	$67.162	$67.16	$67.15	$67.20
Purchase #6	$9.99	8.132%	$10.8024	$10.80	$10.80	$10.80
Purchase #7	$90.27	9.844%	$99.1562	$99.16	$99.15	$99.20
7 purchase totals =	$900.95		$996.4626	$996.46	$996.40	$996.50