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	$218.82	9.278%	$239.1221	$239.12	$239.10	$239.10
Purchase #2	$67.62	4.676%	$70.7819	$70.78	$70.80	$70.80
Purchase #3	$180.69	7.852%	$194.8778	$194.88	$194.90	$194.90
Purchase #4	$93.83	12.346%	$105.4143	$105.41	$105.40	$105.40
Purchase #5	$59.47	10.124%	$65.4907	$65.49	$65.50	$65.50
Purchase #6	$230.95	6.501%	$245.9641	$245.96	$245.95	$246.00
Purchase #7	$142.53	4.491%	$148.931	$148.93	$148.95	$148.90
7 purchase totals =	$993.91		$1,070.5819	$1,070.57	$1,070.60	$1,070.60