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	$78.89	13.304%	$89.3855	$89.39	$89.40	$89.40
Purchase #2	$6.76	11.627%	$7.546	$7.55	$7.55	$7.50
Purchase #3	$132.97	6.656%	$141.8205	$141.82	$141.80	$141.80
Purchase #4	$106.59	4.240%	$111.1094	$111.11	$111.10	$111.10
Purchase #5	$32.86	8.421%	$35.6271	$35.63	$35.65	$35.60
Purchase #6	$239.48	3.104%	$246.9135	$246.91	$246.90	$246.90
Purchase #7	$123.89	5.397%	$130.5763	$130.58	$130.60	$130.60
7 purchase totals =	$721.44		$762.9783	$762.99	$763.00	$762.90