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	$9.79	5.429%	$10.3215	$10.32	$10.30	$10.30
Purchase #2	$19.72	4.642%	$20.6354	$20.64	$20.65	$20.60
Purchase #3	$99.66	6.219%	$105.8579	$105.86	$105.85	$105.90
Purchase #4	$67.69	9.872%	$74.3724	$74.37	$74.35	$74.40
Purchase #5	$124.40	7.605%	$133.8606	$133.86	$133.85	$133.90
Purchase #6	$41.90	10.821%	$46.434	$46.43	$46.45	$46.40
Purchase #7	$35.66	10.610%	$39.4435	$39.44	$39.45	$39.40
7 purchase totals =	$398.82		$430.9253	$430.92	$430.90	$430.90