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	$240.25	6.178%	$255.0926	$255.09	$255.10	$255.10
Purchase #2	$142.33	3.164%	$146.8333	$146.83	$146.85	$146.80
Purchase #3	$155.90	6.688%	$166.3266	$166.33	$166.35	$166.30
Purchase #4	$122.98	5.797%	$130.1092	$130.11	$130.10	$130.10
Purchase #5	$115.34	11.759%	$128.9028	$128.90	$128.90	$128.90
Purchase #6	$41.94	8.660%	$45.572	$45.57	$45.55	$45.60
Purchase #7	$188.99	3.498%	$195.6009	$195.60	$195.60	$195.60
7 purchase totals =	$1,007.73		$1,068.4374	$1,068.43	$1,068.45	$1,068.40