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	$38.66	10.250%	$42.6227	$42.62	$42.60	$42.60
Purchase #2	$250.37	8.238%	$270.9955	$271.00	$271.00	$271.00
Purchase #3	$75.54	9.717%	$82.8802	$82.88	$82.90	$82.90
Purchase #4	$36.69	5.220%	$38.6052	$38.61	$38.60	$38.60
Purchase #5	$245.61	3.158%	$253.3664	$253.37	$253.35	$253.40
Purchase #6	$142.64	6.306%	$151.6349	$151.63	$151.65	$151.60
Purchase #7	$83.99	6.544%	$89.4863	$89.49	$89.50	$89.50
7 purchase totals =	$873.50		$929.5912	$929.60	$929.60	$929.60