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	$71.34	11.577%	$79.599	$79.60	$79.60	$79.60
Purchase #2	$111.47	3.222%	$115.0616	$115.06	$115.05	$115.10
Purchase #3	$85.39	10.437%	$94.3022	$94.30	$94.30	$94.30
Purchase #4	$59.35	10.198%	$65.4025	$65.40	$65.40	$65.40
Purchase #5	$64.77	9.152%	$70.6978	$70.70	$70.70	$70.70
Purchase #6	$169.76	5.630%	$179.3175	$179.32	$179.30	$179.30
Purchase #7	$79.77	13.446%	$90.4959	$90.50	$90.50	$90.50
7 purchase totals =	$641.85		$694.8765	$694.88	$694.85	$694.90