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	$106.47	4.636%	$111.4059	$111.41	$111.40	$111.40
Purchase #2	$42.38	7.651%	$45.6225	$45.62	$45.60	$45.60
Purchase #3	$82.53	6.426%	$87.8334	$87.83	$87.85	$87.80
Purchase #4	$56.64	7.264%	$60.7543	$60.75	$60.75	$60.80
Purchase #5	$175.58	7.829%	$189.3262	$189.33	$189.35	$189.30
Purchase #6	$91.37	6.236%	$97.0678	$97.07	$97.05	$97.10
Purchase #7	$216.25	12.762%	$243.8478	$243.85	$243.85	$243.80
7 purchase totals =	$771.22		$835.8579	$835.86	$835.85	$835.80