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	$143.67	10.117%	$158.2051	$158.21	$158.20	$158.20
Purchase #2	$180.64	4.410%	$188.6062	$188.61	$188.60	$188.60
Purchase #3	$31.81	9.598%	$34.8631	$34.86	$34.85	$34.90
Purchase #4	$47.58	6.843%	$50.8359	$50.84	$50.85	$50.80
Purchase #5	$70.29	10.830%	$77.9024	$77.90	$77.90	$77.90
Purchase #6	$25.74	10.202%	$28.366	$28.37	$28.35	$28.40
Purchase #7	$79.30	13.835%	$90.2712	$90.27	$90.25	$90.30
7 purchase totals =	$579.03		$629.0499	$629.06	$629.00	$629.10