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	$54.48	5.825%	$57.6535	$57.65	$57.65	$57.70
Purchase #2	$108.75	13.656%	$123.6009	$123.60	$123.60	$123.60
Purchase #3	$58.95	11.719%	$65.8584	$65.86	$65.85	$65.90
Purchase #4	$87.61	3.782%	$90.9234	$90.92	$90.90	$90.90
Purchase #5	$193.80	8.343%	$209.9687	$209.97	$209.95	$210.00
Purchase #6	$141.89	11.587%	$158.3308	$158.33	$158.35	$158.30
Purchase #7	$198.70	13.485%	$225.4947	$225.49	$225.50	$225.50
7 purchase totals =	$844.18		$931.8304	$931.82	$931.80	$931.90