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	$5.47	7.500%	$5.8803	$5.88	$5.90	$5.90
Purchase #2	$170.88	4.683%	$178.8823	$178.88	$178.90	$178.90
Purchase #3	$18.46	4.250%	$19.2446	$19.24	$19.25	$19.20
Purchase #4	$50.37	9.817%	$55.3148	$55.31	$55.30	$55.30
Purchase #5	$20.30	10.698%	$22.4717	$22.47	$22.45	$22.50
Purchase #6	$24.86	8.818%	$27.0522	$27.05	$27.05	$27.10
Purchase #7	$133.42	10.821%	$147.8574	$147.86	$147.85	$147.90
7 purchase totals =	$423.76		$456.7033	$456.69	$456.70	$456.80