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	$98.42	4.157%	$102.5113	$102.51	$102.50	$102.50
Purchase #2	$249.86	4.386%	$260.8189	$260.82	$260.80	$260.80
Purchase #3	$180.59	5.226%	$190.0276	$190.03	$190.05	$190.00
Purchase #4	$100.71	10.213%	$110.9955	$111.00	$111.00	$111.00
Purchase #5	$81.26	12.853%	$91.7043	$91.70	$91.70	$91.70
Purchase #6	$49.94	6.123%	$52.9978	$53.00	$53.00	$53.00
Purchase #7	$36.49	11.339%	$40.6276	$40.63	$40.65	$40.60
7 purchase totals =	$797.27		$849.6830	$849.69	$849.70	$849.60