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	$25.91	13.460%	$29.3975	$29.40	$29.40	$29.40
Purchase #2	$57.32	9.275%	$62.6364	$62.64	$62.65	$62.60
Purchase #3	$245.41	8.182%	$265.4894	$265.49	$265.50	$265.50
Purchase #4	$208.87	3.183%	$215.5183	$215.52	$215.50	$215.50
Purchase #5	$91.29	9.828%	$100.262	$100.26	$100.25	$100.30
Purchase #6	$97.67	8.246%	$105.7239	$105.72	$105.70	$105.70
Purchase #7	$202.46	3.779%	$210.111	$210.11	$210.10	$210.10
7 purchase totals =	$928.93		$989.1385	$989.14	$989.10	$989.10