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	$181.92	6.788%	$194.2687	$194.27	$194.25	$194.30
Purchase #2	$128.64	8.505%	$139.5808	$139.58	$139.60	$139.60
Purchase #3	$38.30	6.437%	$40.7654	$40.77	$40.75	$40.80
Purchase #4	$250.29	9.845%	$274.9311	$274.93	$274.95	$274.90
Purchase #5	$82.71	8.446%	$89.6957	$89.70	$89.70	$89.70
Purchase #6	$58.75	5.397%	$61.9207	$61.92	$61.90	$61.90
Purchase #7	$178.96	6.774%	$191.0828	$191.08	$191.10	$191.10
7 purchase totals =	$919.57		$992.2452	$992.25	$992.25	$992.30