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	$145.87	6.529%	$155.3939	$155.39	$155.40	$155.40
Purchase #2	$41.81	13.773%	$47.5685	$47.57	$47.55	$47.60
Purchase #3	$119.45	3.508%	$123.6403	$123.64	$123.65	$123.60
Purchase #4	$78.89	11.311%	$87.8132	$87.81	$87.80	$87.80
Purchase #5	$151.44	12.778%	$170.791	$170.79	$170.80	$170.80
Purchase #6	$71.88	11.497%	$80.144	$80.14	$80.15	$80.10
Purchase #7	$70.55	11.435%	$78.6174	$78.62	$78.60	$78.60
7 purchase totals =	$679.89		$743.9683	$743.96	$743.95	$743.90