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	$148.30	12.539%	$166.8953	$166.90	$166.90	$166.90
Purchase #2	$47.98	8.648%	$52.1293	$52.13	$52.15	$52.10
Purchase #3	$236.31	5.836%	$250.1011	$250.10	$250.10	$250.10
Purchase #4	$88.62	12.220%	$99.4494	$99.45	$99.45	$99.40
Purchase #5	$246.30	10.545%	$272.2723	$272.27	$272.25	$272.30
Purchase #6	$74.82	3.555%	$77.4799	$77.48	$77.50	$77.50
Purchase #7	$35.90	7.211%	$38.4887	$38.49	$38.50	$38.50
7 purchase totals =	$878.23		$956.8160	$956.82	$956.85	$956.80