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	$73.88	13.289%	$83.6979	$83.70	$83.70	$83.70
Purchase #2	$63.71	11.682%	$71.1526	$71.15	$71.15	$71.20
Purchase #3	$135.81	5.425%	$143.1777	$143.18	$143.20	$143.20
Purchase #4	$43.75	11.202%	$48.6509	$48.65	$48.65	$48.70
Purchase #5	$119.29	3.461%	$123.4186	$123.42	$123.40	$123.40
Purchase #6	$6.80	6.766%	$7.2601	$7.26	$7.25	$7.30
Purchase #7	$37.89	13.406%	$42.9695	$42.97	$42.95	$43.00
7 purchase totals =	$481.13		$520.3273	$520.33	$520.30	$520.50