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	$36.87	7.728%	$39.7193	$39.72	$39.70	$39.70
Purchase #2	$54.57	13.782%	$62.0908	$62.09	$62.10	$62.10
Purchase #3	$165.44	12.198%	$185.6204	$185.62	$185.60	$185.60
Purchase #4	$120.25	9.434%	$131.5944	$131.59	$131.60	$131.60
Purchase #5	$105.25	11.409%	$117.258	$117.26	$117.25	$117.30
Purchase #6	$45.75	10.190%	$50.4119	$50.41	$50.40	$50.40
Purchase #7	$172.43	5.117%	$181.2532	$181.25	$181.25	$181.30
7 purchase totals =	$700.56		$767.9480	$767.94	$767.90	$768.00