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	$79.37	13.472%	$90.0627	$90.06	$90.05	$90.10
Purchase #2	$180.86	7.593%	$194.5927	$194.59	$194.60	$194.60
Purchase #3	$141.85	5.723%	$149.9681	$149.97	$149.95	$150.00
Purchase #4	$74.67	5.268%	$78.6036	$78.60	$78.60	$78.60
Purchase #5	$47.81	7.775%	$51.5272	$51.53	$51.55	$51.50
Purchase #6	$175.74	4.374%	$183.4269	$183.43	$183.45	$183.40
Purchase #7	$125.34	4.721%	$131.2573	$131.26	$131.25	$131.30
7 purchase totals =	$825.64		$879.4385	$879.44	$879.45	$879.50