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	$156.57	13.759%	$178.1125	$178.11	$178.10	$178.10
Purchase #2	$132.50	3.525%	$137.1706	$137.17	$137.15	$137.20
Purchase #3	$117.38	9.279%	$128.2717	$128.27	$128.25	$128.30
Purchase #4	$45.59	3.179%	$47.0393	$47.04	$47.05	$47.00
Purchase #5	$50.39	12.411%	$56.6439	$56.64	$56.65	$56.60
Purchase #6	$43.49	7.700%	$46.8387	$46.84	$46.85	$46.80
Purchase #7	$85.62	5.543%	$90.3659	$90.37	$90.35	$90.40
7 purchase totals =	$631.54		$684.4426	$684.44	$684.40	$684.40