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	$38.51	5.370%	$40.578	$40.58	$40.60	$40.60
Purchase #2	$138.70	11.124%	$154.129	$154.13	$154.15	$154.10
Purchase #3	$109.97	7.840%	$118.5916	$118.59	$118.60	$118.60
Purchase #4	$157.91	5.306%	$166.2887	$166.29	$166.30	$166.30
Purchase #5	$156.99	8.467%	$170.2823	$170.28	$170.30	$170.30
Purchase #6	$211.53	12.847%	$238.7053	$238.71	$238.70	$238.70
Purchase #7	$182.85	7.262%	$196.1286	$196.13	$196.15	$196.10
7 purchase totals =	$996.46		$1,084.7035	$1,084.71	$1,084.80	$1,084.70