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	$35.31	12.860%	$39.8509	$39.85	$39.85	$39.90
Purchase #2	$104.78	6.742%	$111.8443	$111.84	$111.85	$111.80
Purchase #3	$35.83	9.865%	$39.3646	$39.36	$39.35	$39.40
Purchase #4	$24.28	8.532%	$26.3516	$26.35	$26.35	$26.40
Purchase #5	$41.73	12.225%	$46.8315	$46.83	$46.85	$46.80
Purchase #6	$184.87	11.601%	$206.3168	$206.32	$206.30	$206.30
Purchase #7	$234.81	12.540%	$264.2552	$264.26	$264.25	$264.30
7 purchase totals =	$661.61		$734.8149	$734.81	$734.80	$734.90