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	$140.68	3.635%	$145.7937	$145.79	$145.80	$145.80
Purchase #2	$81.78	4.174%	$85.1935	$85.19	$85.20	$85.20
Purchase #3	$102.92	13.285%	$116.5929	$116.59	$116.60	$116.60
Purchase #4	$237.37	5.558%	$250.563	$250.56	$250.55	$250.60
Purchase #5	$138.56	13.578%	$157.3737	$157.37	$157.35	$157.40
Purchase #6	$48.43	9.350%	$52.9582	$52.96	$52.95	$53.00
Purchase #7	$74.48	10.171%	$82.0554	$82.06	$82.05	$82.10
7 purchase totals =	$824.22		$890.5304	$890.52	$890.50	$890.70