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	$67.63	5.550%	$71.3835	$71.38	$71.40	$71.40
Purchase #2	$119.89	9.714%	$131.5361	$131.54	$131.55	$131.50
Purchase #3	$40.59	11.511%	$45.2623	$45.26	$45.25	$45.30
Purchase #4	$124.81	10.791%	$138.2782	$138.28	$138.30	$138.30
Purchase #5	$71.59	5.478%	$75.5117	$75.51	$75.50	$75.50
Purchase #6	$44.38	12.746%	$50.0367	$50.04	$50.05	$50.00
Purchase #7	$119.69	6.598%	$127.5871	$127.59	$127.60	$127.60
7 purchase totals =	$588.58		$639.5956	$639.60	$639.65	$639.60