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	$202.26	9.845%	$222.1725	$222.17	$222.15	$222.20
Purchase #2	$79.43	12.486%	$89.3476	$89.35	$89.35	$89.30
Purchase #3	$206.88	8.575%	$224.62	$224.62	$224.60	$224.60
Purchase #4	$118.65	7.431%	$127.4669	$127.47	$127.45	$127.50
Purchase #5	$241.37	6.430%	$256.8901	$256.89	$256.90	$256.90
Purchase #6	$199.75	13.133%	$225.9832	$225.98	$226.00	$226.00
Purchase #7	$155.30	10.677%	$171.8814	$171.88	$171.90	$171.90
7 purchase totals =	$1,203.64		$1,318.3617	$1,318.36	$1,318.35	$1,318.40