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	$99.48	11.599%	$111.0187	$111.02	$111.00	$111.00
Purchase #2	$57.40	13.758%	$65.2971	$65.30	$65.30	$65.30
Purchase #3	$25.56	10.762%	$28.3108	$28.31	$28.30	$28.30
Purchase #4	$58.73	9.361%	$64.2277	$64.23	$64.25	$64.20
Purchase #5	$104.57	7.491%	$112.4033	$112.40	$112.40	$112.40
Purchase #6	$72.83	13.729%	$82.8288	$82.83	$82.85	$82.80
Purchase #7	$230.54	11.873%	$257.912	$257.91	$257.90	$257.90
7 purchase totals =	$649.11		$721.9984	$722.00	$722.00	$721.90