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	$57.25	12.726%	$64.5356	$64.54	$64.55	$64.50
Purchase #2	$164.36	5.751%	$173.8123	$173.81	$173.80	$173.80
Purchase #3	$225.64	6.638%	$240.618	$240.62	$240.60	$240.60
Purchase #4	$61.84	13.857%	$70.4092	$70.41	$70.40	$70.40
Purchase #5	$200.91	7.298%	$215.5724	$215.57	$215.55	$215.60
Purchase #6	$87.25	3.313%	$90.1406	$90.14	$90.15	$90.10
Purchase #7	$68.95	3.557%	$71.4026	$71.40	$71.40	$71.40
7 purchase totals =	$866.20		$926.4907	$926.49	$926.45	$926.40