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	$16.35	3.227%	$16.8776	$16.88	$16.90	$16.90
Purchase #2	$89.85	11.370%	$100.0659	$100.07	$100.05	$100.10
Purchase #3	$196.73	12.350%	$221.0262	$221.03	$221.05	$221.00
Purchase #4	$42.31	6.420%	$45.0263	$45.03	$45.05	$45.00
Purchase #5	$114.54	4.430%	$119.6141	$119.61	$119.60	$119.60
Purchase #6	$199.49	9.625%	$218.6909	$218.69	$218.70	$218.70
Purchase #7	$178.45	5.302%	$187.9114	$187.91	$187.90	$187.90
7 purchase totals =	$837.72		$909.2124	$909.22	$909.25	$909.20