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	$130.50	8.398%	$141.4594	$141.46	$141.45	$141.50
Purchase #2	$40.79	12.690%	$45.9663	$45.97	$45.95	$46.00
Purchase #3	$93.45	12.463%	$105.0967	$105.10	$105.10	$105.10
Purchase #4	$50.88	11.253%	$56.6055	$56.61	$56.60	$56.60
Purchase #5	$165.29	9.253%	$180.5843	$180.58	$180.60	$180.60
Purchase #6	$104.91	11.456%	$116.9285	$116.93	$116.95	$116.90
Purchase #7	$227.39	9.561%	$249.1308	$249.13	$249.15	$249.10
7 purchase totals =	$813.21		$895.7715	$895.78	$895.80	$895.80