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	$7.88	4.784%	$8.257	$8.26	$8.25	$8.30
Purchase #2	$98.27	13.549%	$111.5846	$111.58	$111.60	$111.60
Purchase #3	$204.49	13.507%	$232.1105	$232.11	$232.10	$232.10
Purchase #4	$95.54	3.420%	$98.8075	$98.81	$98.80	$98.80
Purchase #5	$127.90	11.851%	$143.0574	$143.06	$143.05	$143.10
Purchase #6	$153.36	9.106%	$167.325	$167.33	$167.35	$167.30
Purchase #7	$29.86	13.238%	$33.8129	$33.81	$33.80	$33.80
7 purchase totals =	$717.30		$794.9549	$794.96	$794.95	$795.00