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	$103.53	3.682%	$107.342	$107.34	$107.35	$107.30
Purchase #2	$241.52	12.155%	$270.8768	$270.88	$270.90	$270.90
Purchase #3	$146.98	12.375%	$165.1688	$165.17	$165.15	$165.20
Purchase #4	$20.73	13.114%	$23.4485	$23.45	$23.45	$23.40
Purchase #5	$19.87	10.422%	$21.9409	$21.94	$21.95	$21.90
Purchase #6	$132.95	8.352%	$144.054	$144.05	$144.05	$144.10
Purchase #7	$185.91	5.477%	$196.0923	$196.09	$196.10	$196.10
7 purchase totals =	$851.49		$928.9233	$928.92	$928.95	$928.90