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	$141.67	8.705%	$154.0024	$154.00	$154.00	$154.00
Purchase #2	$73.90	5.523%	$77.9815	$77.98	$78.00	$78.00
Purchase #3	$81.53	8.784%	$88.6916	$88.69	$88.70	$88.70
Purchase #4	$54.81	5.627%	$57.8942	$57.89	$57.90	$57.90
Purchase #5	$152.50	13.852%	$173.6243	$173.62	$173.60	$173.60
Purchase #6	$239.79	10.437%	$264.8169	$264.82	$264.80	$264.80
Purchase #7	$82.28	8.194%	$89.022	$89.02	$89.00	$89.00
7 purchase totals =	$826.48		$906.0329	$906.02	$906.00	$906.00