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	$37.71	4.679%	$39.4745	$39.47	$39.45	$39.50
Purchase #2	$130.62	4.417%	$136.3895	$136.39	$136.40	$136.40
Purchase #3	$188.30	4.682%	$197.1162	$197.12	$197.10	$197.10
Purchase #4	$180.71	13.815%	$205.6751	$205.68	$205.70	$205.70
Purchase #5	$217.55	11.476%	$242.516	$242.52	$242.50	$242.50
Purchase #6	$179.90	9.410%	$196.8286	$196.83	$196.85	$196.80
Purchase #7	$154.78	12.120%	$173.5393	$173.54	$173.55	$173.50
7 purchase totals =	$1,089.57		$1,191.5392	$1,191.55	$1,191.55	$1,191.50