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	$49.92	4.133%	$51.9832	$51.98	$52.00	$52.00
Purchase #2	$101.36	9.663%	$111.1544	$111.15	$111.15	$111.20
Purchase #3	$171.57	5.523%	$181.0458	$181.05	$181.05	$181.00
Purchase #4	$99.35	11.805%	$111.0783	$111.08	$111.10	$111.10
Purchase #5	$171.71	4.796%	$179.9452	$179.95	$179.95	$179.90
Purchase #6	$53.44	10.637%	$59.1244	$59.12	$59.10	$59.10
Purchase #7	$124.82	7.651%	$134.37	$134.37	$134.35	$134.40
7 purchase totals =	$772.17		$828.7013	$828.70	$828.70	$828.70