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	$154.87	9.370%	$169.3813	$169.38	$169.40	$169.40
Purchase #2	$82.86	3.268%	$85.5679	$85.57	$85.55	$85.60
Purchase #3	$248.64	12.487%	$279.6877	$279.69	$279.70	$279.70
Purchase #4	$61.30	6.737%	$65.4298	$65.43	$65.45	$65.40
Purchase #5	$50.86	5.489%	$53.6517	$53.65	$53.65	$53.70
Purchase #6	$161.27	12.773%	$181.869	$181.87	$181.85	$181.90
Purchase #7	$37.64	9.754%	$41.3114	$41.31	$41.30	$41.30
7 purchase totals =	$797.44		$876.8988	$876.90	$876.90	$877.00