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	$128.70	7.445%	$138.2817	$138.28	$138.30	$138.30
Purchase #2	$200.56	7.435%	$215.4716	$215.47	$215.45	$215.50
Purchase #3	$147.59	5.535%	$155.7591	$155.76	$155.75	$155.80
Purchase #4	$160.62	5.123%	$168.8486	$168.85	$168.85	$168.80
Purchase #5	$156.99	5.787%	$166.075	$166.08	$166.10	$166.10
Purchase #6	$92.78	10.651%	$102.662	$102.66	$102.65	$102.70
Purchase #7	$229.50	8.852%	$249.8153	$249.82	$249.80	$249.80
7 purchase totals =	$1,116.74		$1,196.9133	$1,196.92	$1,196.90	$1,197.00