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	$18.57	12.742%	$20.9362	$20.94	$20.95	$20.90
Purchase #2	$137.87	7.809%	$148.6363	$148.64	$148.65	$148.60
Purchase #3	$170.72	9.568%	$187.0545	$187.05	$187.05	$187.10
Purchase #4	$214.30	7.262%	$229.8625	$229.86	$229.85	$229.90
Purchase #5	$35.40	12.433%	$39.8013	$39.80	$39.80	$39.80
Purchase #6	$143.50	3.166%	$148.0432	$148.04	$148.05	$148.00
Purchase #7	$142.25	6.215%	$151.0908	$151.09	$151.10	$151.10
7 purchase totals =	$862.61		$925.4248	$925.42	$925.45	$925.40