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	$71.76	7.328%	$77.0186	$77.02	$77.00	$77.00
Purchase #2	$106.71	4.228%	$111.2217	$111.22	$111.20	$111.20
Purchase #3	$130.62	5.221%	$137.4397	$137.44	$137.45	$137.40
Purchase #4	$19.55	3.604%	$20.2546	$20.25	$20.25	$20.30
Purchase #5	$133.31	12.174%	$149.5392	$149.54	$149.55	$149.50
Purchase #6	$219.74	9.863%	$241.413	$241.41	$241.40	$241.40
Purchase #7	$12.81	13.721%	$14.5677	$14.57	$14.55	$14.60
7 purchase totals =	$694.50		$751.4545	$751.45	$751.40	$751.40