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	$38.91	9.610%	$42.6493	$42.65	$42.65	$42.60
Purchase #2	$147.34	11.519%	$164.3121	$164.31	$164.30	$164.30
Purchase #3	$144.38	13.708%	$164.1716	$164.17	$164.15	$164.20
Purchase #4	$177.76	7.197%	$190.5534	$190.55	$190.55	$190.60
Purchase #5	$179.32	9.332%	$196.0541	$196.05	$196.05	$196.10
Purchase #6	$247.94	12.689%	$279.4011	$279.40	$279.40	$279.40
Purchase #7	$240.39	8.753%	$261.4313	$261.43	$261.45	$261.40
7 purchase totals =	$1,176.04		$1,298.5729	$1,298.56	$1,298.55	$1,298.60