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	$39.60	12.816%	$44.6751	$44.68	$44.70	$44.70
Purchase #2	$99.85	11.713%	$111.5454	$111.55	$111.55	$111.50
Purchase #3	$227.25	11.727%	$253.8996	$253.90	$253.90	$253.90
Purchase #4	$100.83	11.190%	$112.1129	$112.11	$112.10	$112.10
Purchase #5	$70.64	11.518%	$78.7763	$78.78	$78.80	$78.80
Purchase #6	$35.99	3.212%	$37.146	$37.15	$37.15	$37.10
Purchase #7	$150.92	3.226%	$155.7887	$155.79	$155.80	$155.80
7 purchase totals =	$725.08		$793.9440	$793.96	$794.00	$793.90