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	$204.82	9.866%	$225.0275	$225.03	$225.05	$225.00
Purchase #2	$176.85	7.840%	$190.715	$190.72	$190.70	$190.70
Purchase #3	$10.32	4.671%	$10.802	$10.80	$10.80	$10.80
Purchase #4	$53.88	13.159%	$60.9701	$60.97	$60.95	$61.00
Purchase #5	$162.63	11.529%	$181.3796	$181.38	$181.40	$181.40
Purchase #6	$38.40	4.307%	$40.0539	$40.05	$40.05	$40.10
Purchase #7	$145.25	4.183%	$151.3258	$151.33	$151.35	$151.30
7 purchase totals =	$792.15		$860.2739	$860.28	$860.30	$860.30