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	$221.93	12.368%	$249.3783	$249.38	$249.40	$249.40
Purchase #2	$77.39	7.549%	$83.2322	$83.23	$83.25	$83.20
Purchase #3	$129.51	10.377%	$142.9493	$142.95	$142.95	$142.90
Purchase #4	$207.85	7.480%	$223.3972	$223.40	$223.40	$223.40
Purchase #5	$31.72	10.707%	$35.1163	$35.12	$35.10	$35.10
Purchase #6	$113.46	12.679%	$127.8456	$127.85	$127.85	$127.80
Purchase #7	$151.95	8.356%	$164.6469	$164.65	$164.65	$164.60
7 purchase totals =	$933.81		$1,026.5658	$1,026.58	$1,026.60	$1,026.40