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	$138.98	12.670%	$156.5888	$156.59	$156.60	$156.60
Purchase #2	$70.95	9.568%	$77.7385	$77.74	$77.75	$77.70
Purchase #3	$67.61	10.327%	$74.5921	$74.59	$74.60	$74.60
Purchase #4	$79.64	4.604%	$83.3066	$83.31	$83.30	$83.30
Purchase #5	$96.84	4.156%	$100.8647	$100.86	$100.85	$100.90
Purchase #6	$52.84	6.689%	$56.3745	$56.37	$56.35	$56.40
Purchase #7	$162.94	3.774%	$169.0894	$169.09	$169.10	$169.10
7 purchase totals =	$669.80		$718.5546	$718.55	$718.55	$718.60