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	$38.34	10.842%	$42.4968	$42.50	$42.50	$42.50
Purchase #2	$118.86	7.239%	$127.4643	$127.46	$127.45	$127.50
Purchase #3	$114.46	5.532%	$120.7919	$120.79	$120.80	$120.80
Purchase #4	$71.28	13.497%	$80.9007	$80.90	$80.90	$80.90
Purchase #5	$44.98	7.459%	$48.3351	$48.34	$48.35	$48.30
Purchase #6	$102.94	10.873%	$114.1327	$114.13	$114.15	$114.10
Purchase #7	$179.31	11.505%	$199.9396	$199.94	$199.95	$199.90
7 purchase totals =	$670.17		$734.0611	$734.06	$734.10	$734.00