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	$137.77	8.454%	$149.4171	$149.42	$149.40	$149.40
Purchase #2	$244.44	3.820%	$253.7776	$253.78	$253.80	$253.80
Purchase #3	$250.40	3.259%	$258.5605	$258.56	$258.55	$258.60
Purchase #4	$88.89	13.247%	$100.6653	$100.67	$100.65	$100.70
Purchase #5	$173.43	9.274%	$189.5139	$189.51	$189.50	$189.50
Purchase #6	$172.32	8.435%	$186.8552	$186.86	$186.85	$186.90
Purchase #7	$238.34	5.126%	$250.5573	$250.56	$250.55	$250.60
7 purchase totals =	$1,305.59		$1,389.3469	$1,389.36	$1,389.30	$1,389.50