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	$243.79	11.649%	$272.1891	$272.19	$272.20	$272.20
Purchase #2	$39.72	4.609%	$41.5507	$41.55	$41.55	$41.60
Purchase #3	$56.83	5.255%	$59.8164	$59.82	$59.80	$59.80
Purchase #4	$223.87	6.302%	$237.9783	$237.98	$238.00	$238.00
Purchase #5	$62.43	9.807%	$68.5525	$68.55	$68.55	$68.60
Purchase #6	$151.98	10.510%	$167.9531	$167.95	$167.95	$168.00
Purchase #7	$35.98	3.397%	$37.2022	$37.20	$37.20	$37.20
7 purchase totals =	$814.60		$885.2423	$885.24	$885.25	$885.40