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	$45.45	7.836%	$49.0115	$49.01	$49.00	$49.00
Purchase #2	$243.89	13.430%	$276.6444	$276.64	$276.65	$276.60
Purchase #3	$43.93	11.118%	$48.8141	$48.81	$48.80	$48.80
Purchase #4	$27.46	4.370%	$28.66	$28.66	$28.65	$28.70
Purchase #5	$94.78	4.478%	$99.0242	$99.02	$99.00	$99.00
Purchase #6	$35.45	10.400%	$39.1368	$39.14	$39.15	$39.10
Purchase #7	$66.81	7.154%	$71.5896	$71.59	$71.60	$71.60
7 purchase totals =	$557.77		$612.8806	$612.87	$612.85	$612.80