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	$144.63	4.605%	$151.2902	$151.29	$151.30	$151.30
Purchase #2	$36.90	3.633%	$38.2406	$38.24	$38.25	$38.20
Purchase #3	$249.99	6.189%	$265.4619	$265.46	$265.45	$265.50
Purchase #4	$40.83	4.584%	$42.7016	$42.70	$42.70	$42.70
Purchase #5	$229.64	3.431%	$237.5189	$237.52	$237.50	$237.50
Purchase #6	$37.35	3.334%	$38.5952	$38.60	$38.60	$38.60
Purchase #7	$48.66	4.292%	$50.7485	$50.75	$50.75	$50.70
7 purchase totals =	$788.00		$824.5569	$824.56	$824.55	$824.50