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	$250.52	9.833%	$275.1536	$275.15	$275.15	$275.20
Purchase #2	$213.45	9.292%	$233.2838	$233.28	$233.30	$233.30
Purchase #3	$222.64	5.222%	$234.2663	$234.27	$234.25	$234.30
Purchase #4	$22.81	8.743%	$24.8043	$24.80	$24.80	$24.80
Purchase #5	$28.89	11.739%	$32.2814	$32.28	$32.30	$32.30
Purchase #6	$195.98	6.339%	$208.4032	$208.40	$208.40	$208.40
Purchase #7	$99.77	3.194%	$102.9567	$102.96	$102.95	$103.00
7 purchase totals =	$1,034.06		$1,111.1493	$1,111.14	$1,111.15	$1,111.30