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	$128.58	6.863%	$137.4044	$137.40	$137.40	$137.40
Purchase #2	$80.52	10.605%	$89.0591	$89.06	$89.05	$89.10
Purchase #3	$79.96	13.393%	$90.669	$90.67	$90.65	$90.70
Purchase #4	$10.71	5.397%	$11.288	$11.29	$11.30	$11.30
Purchase #5	$220.43	4.250%	$229.7983	$229.80	$229.80	$229.80
Purchase #6	$86.55	10.745%	$95.8498	$95.85	$95.85	$95.80
Purchase #7	$7.91	10.699%	$8.7563	$8.76	$8.75	$8.80
7 purchase totals =	$614.66		$662.8249	$662.83	$662.80	$662.90